ECS changed by company after contract is over

I had taken advertising service from Just Dial in June 2015 valid for one year...This is a prepaid service.Since the marketing was giving much result, I discontinued keeping money for ecs debit...Suddenly from Aug they have started auto debit again. These debits are not of the amount agreed...they are sending ecs of various amounts...on contact them they say that the ecs mandate is life long and unless one year money is paid they will contnue to debit. My question is: 1. can they debit more or less than the amount for which they had mandate for..2. can they declare tht the ecs can be debited as per their wish...3. can they debit against an expired agreement..4 i have not renewed their mandate..5. on questioning they have now raised an invoice.