I seem to have got to the bottom of the issue, eventually, with my Malaysian bank.
Despite clear instructions to the contrary they have not been paying your charges every month (but have on some months strangely) (hence the underpayment) and in September their 'system was down' so my direct debit came out a few days late and therefore it appears to have been paid on:
2nd October
29th October
29th November
31st December
I would be grateful if u could check as I looked at the account and no deposit had been made.
Thanks