When my girlfriend became pregnant I decided to sell my bitcoins to decorate a nursery. I auctioned them via localbitcoins. You put your coins into an escrow account, wait for an offer and, when the buyer has paid by Bacs, you release the coins. The buyers are verified by email, telephone and an official ID.

After a couple of days I had an offer. The buyer transferred the funds into my HSBC bank account; I released the coins. The same buyer made another purchase of £530.

Another buyer then offered £6,700 for the rest of my coins. As I attempted to verify this transaction, there was an issue with my online bank account and I headed to an HSBC branch to get things sorted. The manager confirmed I’d received the £6,700 and I released the coins.

After about an hour at the branch I was told that the earlier, smaller transaction had been marked as fraud and the money removed from my account, but there was no problem with the second larger amount.

My account was then blocked for several days. I was informed that the larger payment had also been marked fraudulent and all the payments had been taken from me.

I spent around six hours being passed around by HSBC trying to get an answer. Eventually I was told that I had been the victim of fraud and that the money would be returned. After 10 days my account was unfrozen and I was promised an update. Instead, the account was once again blocked. I can’t get any straight answers. SLW, Bristol

Bitcoin is a virtual currency that has become a fount of free cash for fraudsters. It can be sold on online exchange sites for real money and transferred into the buyer’s virtual wallet, but these wallets are vulnerable to hackers and bitcoin transactions are not regulated so there’s no compensation.

A number of sellers have lost their investments after falling victim to hackers, but in your case it seems the buyers were genuine.

HSBC’s anti money-laundering security alerts were triggered by the unusual sums entering your account, and the bank says it ring-fenced the money and blocked your access while it investigated. Unfortunately you were given mixed messages, for which HSBC apologises. “The funds have been returned, and the account returned to the status it held previously,” it says. “We have also credited the account with £100 as a gesture of goodwill. We will be providing relevant feedback to staff who were involved as, on this occasion, we did not meet the high standards of customer service that we, and our customers, expect.”

If you need help email Anna Tims at your.problems@observer.co.uk or write to Your Problems, The Observer, Kings Place, 90 York Way, London N1 9GU. Include an address and phone number.