Ridiculous Billing

I hve a cellular contract with Altech autopage which i took last year september when i gt it i called in to say decrease my usage limit to O.OO whereby countless times i was told it is.. Next thing i see every month ibgt smses from mtn sayg im nearing my usage limit whereby altech will suspend my line then i hve to call for it to unsuspended this saturday 20-02-2016 they took R2138 from my acc as i pay via do i never received any bill and how the hell can it be R2138 where as every month i pay for the most R600 autopage is a ******* company i wouldnt advise any1 to ever take a contract with them honestly bad poor horrible service even the sales agent never explained how the contract works nothing... My line gets cut every month but my do never bounces I dnw am I a Rich woman or wat for them to take R2138 from my acc altech autopage is horrible disgustingly poor service