I bekei e the agent used the address if the hotel where I was staying. I took photos of me in the room and tge hotel to show local immigration but never needed them.
I can't recommend them as although they did a good job for me 4 times, they messed up my friend and took a lot of money off him and then wanted more. Be careful.
Your problem is in the iPhone. Dump it and get a cheap Samsung with dual sim. Turn them on and off as required. Calls to UK using AIS sim are cheap. Last sim card I bought here was 40 baht and top it up with what you like from several outlets.