Suprise Invoices!

So i got fibre from Easyweb, signed a 24 months contract, signed a debit order so they can take their money on time as stated on the contract, when the first invoice came it showed it was paid for July, but i contcated them and told them that no money was debited forbthat month from my account and they told me no worries everything is up to date, second invoice came for august and also showed that it is paid and i contacted them again that the money was not deducted and they told me again no worries the account is fully up to date, so Today 30th August 2019 i recieved 2 invoices R600 for september and the another invoice for R1198 for july and august that was not paid, i dont think this is fair to me as the customer i contacted them and told them that you guys haven't deducted the money and now all of a sudden i must just rock out R1800 rand?? I mean clearly this was not my fault and thatvthe fault was on their side and that i should not be liable for those 2 months july and august that you they did not deduct as agreed on contract and me as the customer contacted them and told them you guys must take your money they only said they can make a payment plan, so for of ypu out there i suggest if you do decide to go with easyweb as your isp make sure they debit you before you get suprises like me, cannot cancel the contract as it is a 24 months but for those out there what would you think they should have done ? I think they should have just written those 2 months off as it was their fault and only started billing me from now on, Bad service if you ask me!!