Cancelled is not the same as rejected. Normally applications are cancelled as there is something wrong with the primary data such as name or passport details

@Richard *******

you have trouble reading?

Sounds like they did their job correctly. Visa exempt is issued for tourism not for living in Thailand with your girlfriend. You need to find a proper visa that you can apply for that allows you to spend extended periods of time in Thailand. You don't look over 50 and your not married so your main options are the DTV or the Thai Privilege visa, other than that get a job or sign up for a course of study (which you'll need to actually attend and learn)

Show both passports on entry then visit immigration to get the stamps moved from the old passport to the new one

You don't have to get the DTV from your home country so you could consider coming to Thailand using a visa exempt entry to get a consultation and treatment plan at the hospital you want to use then travelling to a nearby country to apply for the DTV

Best you speak to the BOI as they are the ones responsible for issuing the LTR visa

@Joe *********

correct

You need to have registered with your immigration office then ask for a certificate of residence

The first thing to note is you can't get a DTV visa inside Thailand. You need to apply at a Thai consulate and there aren't any in Thailand so be very wary