A 55-year-old factory worker claims his life savings have been "taken" after being convinced to plough his pension into storage pods.
Robert McCarthy, of Ebbw Vale, said he has lost more than £30,000 through a Self-Invested Personal Pension (SIPP).
The Financial Ombudsman has received 150 complaints from Wales against various SIPP providers between April and December last year alone.
Berkley Burke, which administered the investment, has been asked to comment.
The Leicester-based company is facing at least 500 similar complaints.
Blaenau Gwent MP Nick Smith is calling for greater consumer protection.
Figures show complaints to the Financial Ombudsman regarding SIPPs, known as the Do-It-Yourself pension, doubled between 2016/17 and 2017/18 from 1,025 to 2,051.
Mr McCarthy, who worked in a battery factory for 13 years, wanted to move his pension from the company scheme in 2011, after it slumped following the 2008 recession.
He contacted Liverpool-based company, Jackson Francis, who offered attractive pension investment options via the pensions administrator Berkley Burke.
That included putting his money into Store First - a company offering storage pods, with returns based on rent paid for using the pods purchased.
However, according to Mr McCarthy, the company failed to explain any of the risks of the investment.
He told BBC Wales Live programme: "He [the representative] said this would be the next big thing throughout the country. The way he put it over was, by investing in store pods you would be making money all the time."
But in 2017, Mr McCarthy became concerned when an unexplained letter from a solicitor in North Shields arrived, asking if he had problems accessing his storage pods or finding out about the current state of his investments.
He then discovered the unregulated company, Jackson Francis, that initially introduced Mr McCarthy to Berkeley Burke and Store First, had been wound up in 2014.
He said: "I phoned Store First, and a lady said 'Your store pods are empty.' I said 'What do you mean they're empty? They can't be.' She told me they'd been empty for two years… Nobody had contacted me to tell me."
Store First said they were never contracted to manage, advertise or let the storage pods - that responsibility, they say, lies with the pension trustee, Berkeley Burke.
It said: "Mr McCarthy has not purchased any store pods direct - he has instead arranged for a trustee to buy them, as part of his self-invested personal pension.
"We have asked the trustee, on two separate occasions, if they would like Store First to manage their store pods.
"The trustee has not however returned the management agreements we have sent to them. That is entirely within the power of the legal owners of the store pods. Store First cannot, and would not want to, force any investor to use Store First's services to let out their store pods.
"If Store First is not engaged to let out the store pods of course, then it will not be paying any money to the investor - they will need to find customers themselves."
The UK government is currently petitioning to have Store First wound up in the public interest.
In the High Court last October, Berkeley Burke was found to have failed to show due diligence in vetting unregulated investments for another client. The company are currently seeking to appeal against the decision.
Hugh James Solicitors in Cardiff are representing 14 individuals from Wales, including Mr McCarthy, in further complaints against Berkeley Burke.
Solicitor Richard Evans said SIPPs are often unsuitable and administrators must take more care in assessing investors.
He said: "These people are not sophisticated investors with vast portfolios. They are individuals with a pension pot which they worked very hard all their lives to build up.
"We say Berkeley Burke have not conformed with what their duties should have been."
Blaenau Gwent MP Nick Smith called for greater guidance for people seeking to move their pensions.
He said: "Work needs to be done from the perspective of the consumer, for the pensioner who isn't sure how to invest their money, that doesn't know where to go for guidance, who isn't clear who is trustworthy and who needs support in understanding this complex financial world."
Mr McCarthy has now started to rebuild his pension for him and his family.
However he added: "Basically I've lost my private pension. Thirteen years of hard work, they've taken it, it's gone.
"I'll never trust anyone again. And I can't believe that they can get away with what they've done."
For more on this story, catch up on BBC Wales Live.