Sorry you didnt have a good experience.

Even e-tickets do generate a receipt for your travel. You should have been emailed this when the booking was ticketed. It is common for FFPs to ask for receipt when pax makes a missing mileage request for travel on another airline.

FWIW the bassinet row is marked as such on SQ's seat maps, and I think when you select the seat (at OLCI in this case) it even brings up a warning that you may need to be moved. On most airlines the first economy row is for bassinets.