Contract Ended

I had a contract and when it was ending last year I decided not to renew it. I called customer service in advance and informed them of my decision. Well everything was fine on the phone and I was told that it is done I'll be on prepaid. The following month I was debited more than double of what I paying on contract. I disputed the debit and phoned cellc. I did not receive a satisfactory explanation of the doubled amount but I paid it anyway. Last week I find out through credit check that apparently I'm owing cellc,several months of non payment to the service provider. I called cellc, again no explanation for why I wasn't informed of any outstanding debt. I don't even know what for. I paid it anyway and I was promised to receive a paid up letter within 1-2 days, that was a week ago till today nothing. I've phoned customer service service several times and after being put on hold for more than 10minutes the line goes dead, I've sent emails still waiting. After 17yrs on contract with cellc this is the thanks i get for being their customer.