Nakhon Phanom immigration insisted on 3 months before extension application. I was three days short and had to go back the following week. Always check with your own office.
Nakhon Phanom does not issue RC for anything to do with motor vehicles. I have to go to LTD and they request what they want from immigration. Takes about two weeks. Not saying your office is the same but ask at DLT. Dint forget the medical certificate, one for car and one for bike license. My copies were not accepted. Even though ink jets are pretty good they check for indentation on back! I've tried it but only got away with it once. Blue ink too on official forms.
cost if calls to UK landlines is about 5 baht per minute. To UK mobiles about 8 baht per minute. My UK sim wants £1.75 per minute! My only advice is to do all you can to avoid your UK bank thinking you live in Thailand. I made two monthly Swift transfers and my last account was closed. In addutionnyte bank messed one transfer up completely meaning I had to start 12 x monthly payments again.
44 with no + is very cheap. Maybe the best way to call your banks. Why not order a contract sim from uk and use that when you need to receive pin? That is what I do and it works well. Just make sure your uk number us registered as +44 something or it might not work. Dual sim phone allows you to keep thai sim fitted at same time for normal use. I use talkmobile at £11.75 a month. Might sound expensive but I get use of phone as soon as I land in UK and vv in Thailand.