[Closed] Potential problem with mobile supplier.

Due to my previous foreign address, I couldn't get a contract mobile without a deposit. All good so far, I paid the deposit and got it written on a receipt but I think it might have been a cash deposit, without looking I can't be sure.
Anyway the six month period is up and they should have returned it. I spoke to customer services and they've told me that there is no record there. 😯
Anyone had similar and was it resolved quickly and easily? Or did it become a bitch fight?
They've said they'll get back to me in 48 hrs, how long should I wait before getting upset and shitty?
TIA.