Awful credit card

Nationwide Credit Card.
On holiday in early April (N/Wide aware) and wanted to use debit card for cash withdrawal.
Worked once then no more (3 accounts - all in credit).
Had to resort to using N/Wide credit card.
I knew this would incur a transaction fee etc and some interest.
2 withdrawals of £63 each (limited to this by local rules) and 2 fees of £3.I also used the card to make 2 purchases totalling £97.
Returned home and paid off £250 immediately to avoid too much interest as have a 0% deal running currently. Charged interest on next Statement. Paid further amount (£100 to reduce balance (minimum is £25). Thought that would be it as far as interest is concerned.
Received next statement and charged interest again on both the cash and purchases.
Rang N/wide to clarify. Answer was that charges are applied at the end of the statement period and payments were too soon so were taken off the main balance and consequently the interest was charged for the 2nd Month as well. The payments appear on the statement before the fees!
I asked if the payment made the following month would cover the cash element as it was the highest interest rate (32 % APR). Was told no, there would still be a further charge as the fees weren't paid from the previous statement.
It seems (confirmed by N/Wide advisor) that you can't avoid any of these fees at all and they will continue for, at least, 2 -3 months afterwards regardless of how much you pay.
The end result is that because N/wide blocked my debit cards (despite having registered that I was going abroad and supplying dates and destination) I had to use my credit card.
I am not too concerned by the cost (£10 to £15 - hopefully) but am irritated by the process and having no way to avoid this.
Nationwide has had many good points in the past but this makes me wonder if their move to "normal" purely for profit banking is coming soon.
They did, after an hour on the 'phone, offer to refund the interest charges of around £4 for May but these haven't yet appeared on the account!
I fully expect to be charged again.