DH and I have a joint credit card and usually pay half the balance each - we always pay it off in full each month. This month we accidentally underpaid the balance by £50 - not sure how. So the full balance owed was £3000 and we only paid £2950 in total. Got the bill this month to find we have been charged £65 interest! The apr is 23%. We have queried it with the credit card company who say as we didn’t pay the balance in full we have been charged interest on the entire amount we owed last month - ie £3000. Can that be right? Surely it should just be interest on the outstanding balance - ie £50?