I think your advice about how to get a fake flight statement can be considered fraud by a consulate. This is really not the paper they ask for. You need a confirmed flight. Also know that they can check the validity of a booked flight online at most airline websites.
I was able to open an bank account inclucing internet banking and a debit card with Krungsri bank with a 1 year rental contract. I also opened a Bangkok bank account. But it was more difficult and for some reason they did not want to give me access to internet banking.
It's not just now. When I hear the word Qatar, the first thing I associate it with is cancellation. Maybe you can try Air France KLM (Delta in the US) or Etihad?
2 years ago I went to Thailand, got a VE at the airport, but my ticket back was 2 months later. It was no problem. But they didn't check. I got a 1 month extension in Bangkok.
" sim card ... unlimited traffic ... 900THB per month" That is very expensive. On Lazada there are deals with 4G sims, unlimited traffic 10mbps for less than 2000 Baht a year. Search for "true 4g 10mbps" many 1890 Baht a year offers, or "ais 4g 8mbps" also many 1890 Baht a year offers.