Not doing a 90 day report does not put you on overstay, you just get a 2000B fine for reporting late so, in your case, you shouldn't have reported because once you're late the fine does not increase. Report late next time and it's another 2000B.
Sorry, you said you've done it before. To make it easier to fet a bank account it would help to get a Non-O before he travelled otherwise it would probably need an agent.