In January I called them to cancel my contract so the lady who assisted said it's better to downgrade and not cancel so I get to keep the number

In January I called them to cancel my contract so the lady who assisted said it's better to downgrade and not cancel so I get to keep the number. We agreed. Last month the allocation was fine and correct. Now this month instead of allocating they even took the airtime balance I had. No allocation for the month, remaining airtime is also gone. Call centre said they allocated but don't know what happened. They will check and revert, how is it possible that 01st of the month midnight airtime is zero til now 19h30. They should rather cancel the contract. This is *****. I don't even have subscription in the background.