Deposit Refund on rental

I’m tired of trying to get my deposit back from them, I hired a vehicle and I was told upon return I’ll get my deposit back it’s been more than 30 days.. no response to my emails and I’ve tried calling.. last email I received from them was “please assist customer about refund” something along those lines... Im now having to use my own airtime and internet to try find out what’s going on and still I don’t know, I haven’t even received an invoice.. they have been very unprofessional.. if they don’t want to give me my money they should just say