No. not in Thailand. You’d have to visit a Thai consulate outside of Thailand. You’d need to check with their website to see if you’d be eligible to apply there.
If you’re from India, Sri Lanka, Bangladesh, Iran, Nepal, Togo, Nigeria or Uganda you cannot get an extension off a single entry tourist visa. I have no idea why. Indian nationals who come in visa exempt can get an extension. Go figure.
There are countries that won’t allow you to visit them if you have a stamp in your passport for another country (like Israel and Egypt) but they are few and far between.
Ah. So you didn’t get the METV at a consulate that is not your home country. Like every other human on the planet. You say that they said you could but you didn’t. Enough said.