Thankyou all for your time and answers i will get busy writing to the relevant authorities. If i get any futher letters from these 'people' should i ignore their demands and simply file the letters?

Hello, im new to this. I will try to explain fully so i can hopefully recieve some helpfull advice. In August 2009 i recieved a letter from 1st Credit looking for someone with a very similar name to mine that previously lived in Bournemouth. As i am not the person they are looking for i phoned them and tried to explain this fact, as i would not supply any personal information the phone operator basically told me that this was an admission of being the person they are looking for and that futher proceedings would take place. I witheld my telephone number so they have not phoned back. I wrote a letter (i have proof of postage and delivery) to 1st credit explaining that i am not the person they are looking for and that i have never lived in Bournemouth or even in the county of Devon and that i have medical and financial records to proove this. They have ignored this letter and now have sent a letter stating that they have been assigned to administer an account of outstanding debt of £18,500 on behalf of a major high street bank and i should pay up. I do have an account with this bank but am not nor have i ever been in debt to anybody. I contacted the bank who informed me that i am correct in that i am not nor have been in debt with them but apart from that were of little help. I have had to see my GP as £18,500 is a lot of money to me and as i am on long term sickness benefit and this letter has caused me more worry and grief. Please any advice would be most helpfull