MTN DATA ripoff

I've been on a 40GB data contract with MTN for 16months now where any unused data would carry over to the next month and was valid for 60 days according to the information I was given, now it turns out my contract does not have the carry over as previously informed , this comes after a whole month (November) of unused data was not carried over as usual. When I called in today I was told that my contract runs on a 30 day period and any unused data gets forfeited.... So I then requested the contract to be cancelled and was notified that a penalty fee would be charged as I'm cancelling before end of contract which is understandable, but now the fee must be paid first before the actual contract can be cancelled, this does not include the debut order that ran yesterday on my account for the month of December and I would forfeit the data loaded that I actually paid for.

Why I am subjected to pay before cancellation but my monthly data gets loaded before payment