Very bad service

I am very disappointed with MRP Mobile, the way they handle their clients and contracts is quite disturbing. I took a 24 month cellphone contract with them and after 24 months they automatically renewed the contract and have been doing that for years. The problem has been trying to cancel the contract. Everytime I cancel they tell me I owe them and after I have paid they assure me that the contract will be cancelled and it never happens. Early June a put in a request to cancel the contract and I was told the account was in arrears and they suspended the phone. They told me to pay the outstanding amount then the contract will be cancelled. So the debit order went through on the 25th of June, shortly after that I received an sms threatening to blacklist me for not making payment. They even called asking me to send them proof of payment via whatsApp, I also took the liberty to emai the proof of payment. They kept quite for a while after that, I called them and was told the amount had not been allocated and that they would allocate soon. Yesterday I received an email saying " Kindly note the contract will be successfully deactivated and the sim card will be converted to a prepaid sim on the 1st September 2019, you will be liable for payment of the July and August 2019 invoice, provided there is no unbilled usages in that current month". This is disturbing to me because they had assured me once again that once payment has been received, the contract will be cancelled since I did give them a 30 day notice. Now they expect me to pay again for July and August. I do not even understand why I should make payment for 2 more months. Their reasoning is that their payment was allocated late therefore they cannot cancel the contract for July and because their cancellation date is 1st of every month then I am liable for July and August since the 1st of August falls on a new month. I am sick and tired of this exploitation and I am at this point willing to take legal action. I have emails indicating my request and sms's threatening to blacklist me.