I ordered a sim through Topcashback on Saturday and it didn't appear in TCB until Wednesday, so don't worry about it yet.
If it's not appeared after a week you should raise it with TCB.
It's been a week and it's still not on TCB, I've raised it with them but I will go over my 14 days cancelation period soon. I will cancel it at 13 days if I don't get the cash back.
I've also orderd another one for my daughter. Different browsers and all of that and it's not tracked.
I've never had problems with TCB before.