Can't believe the post office work with these crooks

Tried to make a transfer using my Natwest card. Failed on three attempts with no error message - almost locked up my PIN. Later I find out that they don't deal with Natwest...
Then I used a Euro debit card to make the transfer, all seemed fine. Then I get a phone call saying that the transfer hadn't gone through. OK I said I'll make alternative arrangements and made the transfer via my wife's bank account. I then get an email telling me that I have to pay the difference in exchange rates because they had bought currency for me.
1. Why would they buy currency when I haven't paid them?
2. If the exchange rate goes the other way would they pay the customer a bonus?
3. Apparently they can't work with Euro debit cards but still did the trade!
4. I wasn't told the money hadn't gone until 5 days later - my daughter needed it urgently
5. They got the business anyway via my wife
6. I received a letter today from a debt collection agency

Crooks to be avoided and the Post Office is damaging its reputation.