Billing for a prepraid number

I have been paying every month for a cellphone contract that expired in 2 June 2015 and I did put in request for the number to be on prepaid at the end of the contract period and that was done however every month money is deducted for this number that is currently on prepaid and I'm not using the number at all as I was told not to use the number until this is resolved but now I keep on getting messages saying the case number has been closed and I don't understand how can case numbers be closed while the issue has not been resolved, every month I get new case as I always have to call and complain about the same issue every month and the answer will be the matter will be escalated and we will get back to you and nothing has been done up until now.