Unathorized debit ordeer

I made agreement with FNB collection 2 weeks ago that they should debit R1800 every month from my account.. on the 27th I woke up to a notification of R4324 , I went to FNB Bank city to enquire, they gave me FNB loans number that are useless you will hang on until you ran out of airtime.. the following day on the 28th , I got another notification of R1638 from the same FNB..made calls , a lot of them no one wanna account.. Ill leave their account with peace and join standard bank, I wont pay the rest of the credit until they sort out this mess ...