They debit more amount than agreed amount

I am very disappointed by the service that I am receiving from tracker. I have been making payment as usual for the amount that is agreed between us. My Debit order is agreed to be the second of every month for the amount of R257. But the worst experience started to happen in February where they started to charge me R570 which I didn't understand where it was coming from because there was no new arrangement or notice for the increase. I refused to allow such debit order to take place because it's not the agreed amount. I owe two months which is February and March and the total amount is R600 or less but today they Debited R1200 for two months. This is a **** because we never agreed to this new amount that I taken from my account. This is really disturbing and is costing me bank charges. They must make sure that this fix mess or else il look for a new tracker. I am really ****ed because this mess keeps continuing.