I've suspected that besides proof of a matching Thai ph#, since they always request passport for ID and to photocopy multiple times - as soon as they see no current long term visa, the result would be making you close the account. ☹️
Mail was supposedly the only method then too. You might want to check your statement unless you've confirmed with the embassy that they no longer offer in person services.
I'd ignore all the suggestions to get a retirement visa. If you're only looking for a 6 month stay, there's no reason to go to the effort - that's for retirees who want to stay at least a year. Also, it requires exchanging/transferring about $30,000CAD or proving you have enough monthly pension income. Really too much work if you're only planning on 6 months.
Right now there's still a visa free 60 day on arrival (can easily extend for another 30 days at any immigration office in Thailand). Normally if you leave to visit another country for a week and then return, you could do that a second time (6 months total). The 60 day is supposed to be going back down to 30 days though, so if that happens then maybe the DTV.