Airtime ****

I've had a data contract with vodacom 2 years ago, so since well it was ending this year, I wanted to cancel it however the consultant convinced me to keep it as airtime top up of R85 and I will be paying R80 for it. His explanation was that I could go and upgrade or cancel it anytime. So my services were blocked since August the 28th, until I made a payment from August till date. When they unblocked my service, they only loaded R80 for one month, they didn't back pay for other months and when I made an enquiry regarding that they said it's because my line was suspended, but why did they make me pay for the months that they didn't make provide a service for? I paid for something that I didn't receive, that's a ****. I'm not happy with this, they should reimburse me for the months which they didn't provide airtime for or else I'm canceling this contract .