Thanks PossVox and Pinky69 . I will send them a letter with payment . Just one more things I wounder ,I havent contact 3G mobile for 3 years and I have moved home 2 times. How do they find me?

Hi there, I recently recived a letter from a company called lowell protfoliot 1. They informed me 3G mobile company have sold my account to them on 30/06/2008 , and I need pay them the outstanding balance of 34.97 pound. I wasn't sure about it.I did have a 3g mobile contract before and it end 3 years ago. Then yesterday I found the last 3g phone bill and check my bank statement . I didnt pay 3G last 34.97 pound.The ref number is correct on lowell's letter. I did search online about lowell protfoliot 1 and I found some people have trouble with this company .Some people suggest dont call them (dont giving the personal detail to them) or ignore them. I think I need pay the bill ,so can I call them or send a letter with money?. Please ,please ,please give me some suggestion. Many thanks Vic