I mucked up my last credit card repayment.
I normally repay the whole amount and pay no interest, this time I misread the amount and repaid $37 short of the full amount.
I was charged $153 interest
.
I spoke to a nice lady at the bank (which bank?) who showed me the fine print.
It seems that interest becomes payable on the whole amount, plus anything accrued since that date.
After politely making it plain that I wasn't happy (understatement) and leaving the bank before I said anything I'd regret, I got a phone call from the nice lady who informed me that the interest would be reimbursed.
Needless to say, I'll be making doubly sure that that dammed card is fully paid off in future.
I got lucky once with the bank, I don't expect it'll happen a second time.