Money owed after 7 years on LG K220 ***)

In 2006 I took a cellphone on contract. My contract expired in 2008, I called to cancel I was told to submit the cancellation letter in writing. I went to our local store and submitted a letter. When I followed up, I was told that the store never submitted my cancellation. I went back and was told that the store doesn't accept letters which surprised me, but I still e-mailed the cancellation letter. <br> <br> I didn't hear from Cell C again and even went to change the number from a contract to a pre-paid number as it was done then. I then got a call, the consultant advised me that I'm owing Cell C money for my contract (which to my knowledge was cancelled). After this, 3 more letters were mailed to Cell C and then recently I got a call advising me that I still owe them R5 400 but if I pay cash it would be R4100. <br> <br> Now, this all happened in 2008, therefore I do not have the original letter but I'm sure with all the calls I got there should be voice recordings which will confirm that my letter was received, also all the other calls should be there. I've been listed on the credit bureau, this is unfair and if this query is not resolved, I will have no other option but to go to the Ombudsman.