******* and ******s

We have no choice or alternative. That is the worst thing about it all as we have no way of voting with our feet. I have accidentally paid money into an account that is not active and have been struggling for over a year to get the money refunded. Every time I write to them, they request documentation, which I send, only to hear nothing back. When I write to follow up, I get a new reference number and people asking for the same documentation, which I provide again and again, nothing happens. It's been going on like this for a year. What can I do?