Debenhams/Santander credit card

Hi, not sure if this is the right place to post. In October a Debenhams/Santander credit card statement was received at my address. It was addressed to someone that I'd never heard of and that has never lived at the address. I opened the envelope as the Debenhams logo was displayed and I do have a Debenhams account. I checked the account number which was not the same as mine but there was an outstanding balance in excess of £1,000. I contacted Debenhams but as I was not the named account holder they would not discuss the matter with me. I was told to return the letter stating the named person did not live at the address.
In November a further envelope was received and promptly returned. Last week another envelope arrived - this was opened and it transpires that 2 payments have now been missed! I rang them up and was again told to return the letter as they couldn't discuss the matter with me. I asked to speak to a supervisor/team leader and after holding on for ages was told that there wasn't one available.
Can anyone offer any advice on how to resolve the matter and get Debenhams/Santander to look into this and stop sending the statements to my address? I am very concerned that if this is not resolved quickly that my address will be black-listed and that it could affect my credit rating.
Thanks a lot.