Vodacom Contract Issue

hi, i had a 24monhts contract with Vodacom, when my contract came to end in May 2021. In June i noticed that it was still active so I gave them a call to find out if the were not supposed to stop or cancel the contract as per our contract agreement. I was notified that i had to give a months notice which I don't understand why it has to be my responsibility to notify you (Vodacom) that hey my contract has came to an end when there should be a process in place. So when the debit orders came off my account for July and Aug I reversed them because I really felt the agreement I had with Vodacom ended in May and I did not not sign up for any extension after the contract had concluded. I would like to find out if am at fault for not willing to pay the amount occurred after the contract had expired mind you I had called more than 3 times to notify them of my cancellation