I personally wouldn’t touch AMS if I can avoid it for the next few days, it’s utter carnage with people being stuck there for days now. If you can disembark in Fra call BA as others have said and see if they are happy to rebook you from FRA, there may be some flexibility as nearly every flight is canx again today. If not and since it’s an Avios ticket leave it and rebook from FRA, your “new flight” may get cancelled too and you get everything back, if it’s not as you say it’s not a huge loss fincancially and write it off.

if QR insists on getting you to AMS go with it, send receipts for hotel in, as already suggested.

Good luck and let us know how you get on