Cell C ripping me off

I had a very bad experience with this service provider last September I bought Samsung J4 installment was suppose to be R199 every month but 1st debit they took R365 2nd debit R468 3rd debit R486 my point is they haven't debit our agreement even last month they debited R465 so I fail to understand how they work they ripping me off.I'm so fed with this whole situation.Today I got a message from them telling me I should have R462 in my account because they going to debit that amount at the end of this month