It happened to me too.
In the UK, they will allow you to board the flight, in Doha, they go by the book (can't think out of the box).
In a similar situation as yours, I had no choice but to buy a new ticket at the airport and then later on, when I presented the missing credit card, they reimbursed it to me.
Still the mystery remains why in the UK and Qatar the procedure changes even if it’s the same airline!