Cancelled contract still active

I called to request cancellation of a data contract in April 2017 and got rid of the sim card. Few months later I saw that I was still being billed. I called the call center and was told they need to go through records to confirm that I made the request and will call me back between 7 - 10 days. I didn't hear anything and called the call center back, I was told to get a new sim and utilize the accumulated data and that they would transfer me again to do a cancellation, when transferred to cancellations the line was dropped. When I went to get a new sim card with the accumulated data I was told the data was month to month.

Please can this be addressed urgently, either a refund or the usage of data that has been built up since cancellation was requested.

Very frustrated with the terrible and inconsistent service.