terrible service from Motovaps

I had a plan with Motovaps from May 2017, and I serviced my car last year April 24, 2018, and when I come for service this year I was told that my service plan is no longer valid and I was not aware as I was not even reminded that I skip the payments because I authorized them to deduct their money on monthly basis, but only to find out that when they were upgrading their system they made a mistake with my payments, again I was not even told but now my car is due for service I was told to pay R1500 before it can be valid, I have the following question to them 1. who told them to stop deductions 2. why I have to pay while I'm not at fault 3. if they can't pay for my service I'm requesting them to pay back my premiums form April 2018 until October 2018