Difficult situation with a difficult client meant I had to change a flight last night (ex-EU itinerary to the US booked on ba.com if that's material).

After two hours on multiple phone calls to/from BA, it got priced, paid and when I got up this morning it's ticketed, seat selected and all looks good.

BUT I have no receipt for the change fee of €300. I've had no emails at all about the change. I went to MMB and requested a receipt, which gives me receipt for my original payment but showing the new flights, which is no use to me as it reflects neither the original nor change transaction payments.

The difficult client won't reimburse anything without receipts. Last time I had to ask BA to raise a manual receipt when I didn't receive one originally, it took two months and I ended up being out of time to claim it from the client so ate the cost.

How do I get a receipt for this transaction? It's bad enough I'm getting screwed around by this situation, but I really don't want to end up paying for the privilege!