Disastrous service

Tried to take mobile account and I was looking for an amount around R1000 or R2000 however it gave the R7000 full amount and no option to change to a lesser amount when I pressed on the amount nothing happened it send no withdrawal nd when went further it just confirmed the full R7000 amount and was asked to agree to bank mandate I did not agree to the bank mandate however the proceeded with the amount and now the say I can't cancel the loan and there is no cooing off period , I want is to cancel the loan because the installment are to high but they said when called that my problem and it has nothing to do with finchoice