Fuel Cap snapped off while filling up

[PetrolnEWB]

Hello all, my grateful thanks to forum users who advise me with this issue. So I was filling up my Ford fiesta 2011 a few days ago and as I removed the pump the bloody cap snapped off with it. Whats worse is that when I try to fill up the car, the pump stops every few seconds. seems like something could have dropped inside the tank, unless the pump will not work while the cap is broken. Any advice on what this part if actually called, links to diy fixes or advice would be greatly appreciated. Being a student and all Im not sure that I can afford much of a financial hit, unless it wouldn't be an expensive fix?

Thank you in advance!