Bad service

I open up a contract with you guys a couple of months later I decide to cancel I called the contract department got a cancellation fee paid it call to confirm the next day they said I must another outstanding amount I did that and called again the next day I see my phone was on prepaid I still got my proof of payment and couple a months gone I get a sms about I been handed over to your debt collectors and say I owe so much and yesterday I get called that I should make a payment before month end and so I'm waiting for them to debit the amount and what about the money that I already paid because I explained to the operator but he said I must pay again and I was promised 30 gig free I only got 20 and my Zando voucher did not work I'm still waiting for your reply on since the day I open the contract