Bad Credit due to Bad Service

I used to have a Virgin Mobile Contract. I tried to end the contract, and followed the prescribed procedures. I then received notice that Virgin had handed me over to debt collectors for an outstanding account. I have been fighting with them for over a year, and they have now threatened me with legal action. <br> <br> They claim that they had attempted to make a deduction from my account after I had cancelled the contract. They further claim that the deduction was returned as being unprovided for, or that I had reversed the charge. I did no such thing, and there is no such record of any such transaction on my bank account. I now have a bad credit rating, and I am fighting with their legal department, as they are threatening me with legal action.