Interest charged

Pay just now is a **** in my opinion.this no interest thing of theirs is a lie.i made a purchase last month and on the 26 my account didnt have funds.i sorted that out today and made payment only to find out they deducted R920 instead of R775.i dont understand how missing a payment by 6 days warrants taking R145 extra feom a client.iv had no issues before and have used the app for a long time