Impossible to get a refund

I have been waiting on a refund for an early termination of contract charge since July. I sent my new proof of address that Virgin don’t serve my new area in time, but they still took the money. 

I have been promised multiple times since then that I would be refunded via cheque or bank transfer, I wait the amount of days they say it will take, and the money/ cheque never comes. When I phone again the customer service person agrees with me that I’m owed the money but can’t explain to me why it never comes through. I am at my complete wits end.