I was given a discount to settle the account

I had mr price mobile account in errears,of which i was given a discount of R802 to settle the account within two months,we made the arrangements through debit order,the first months they did debit R401 and send the statement later that i am left with R567.67 then the second month the did debit R401 again of which i was supposed to be done paying the account off but i kept quiet and now again they come back and say they will debit R212 and of which i can't tolerate this anymore.please Please peter intervene.