what are the chances of getting it back?

[intgol]

i sold an old samsung phone to a cex like shop just over a week ago, as soon as I sold it i had to go to the airport as i was going away for a few days for work.

realised mid flight I had left my sim card in the phone when i sold it (i have two, one for work one for me)

unless they have sold the phone already is it likely to still be in it if i go back and explain? i would just order a new sim from giffgaff but i can't log in as its asking me to confirm the number on my account which is the number on the sim in the samsung!

Phone the sim card provider and report it as missing/lost, which it is. The sim will be cancelled and they will send you a new one. If you give them the phone number for the sim they must be able to identify you by some other means, security questions for example. Your account number is not on the back of the sim.