Over over charged

I feel that I'm being ****med because i couldn't pay my last payment of R666.68 for the 5th of Feb, now Pay Just Now do debit every week in my account from the 5th i don't dispute the charging interest why do it weekly while im paying monthly. It R811.66 then R956.66 following week now is R1, 101,66 this week. I'm not working and my son will only give me R1000 i didn't even wanted to open the account and they told me they are using my son's son's account for debit but their system denied that and now I'm in this ******ion position please help.