I just got a Non B in London.

It states the company I would be working for above it. I have been offered a better position with a different company.

Am I able to use the Non B to apply for an extension and work permit with "Company B" even though it says "Company A" on my Non B?

Thanks,
James

You would likely have problems applying for a work permit and a extension of stay at immigration due to your employer not matching the one shown on your non-b visa. You would need to get permission from the employer shown on the visa to do the applications.

Thailand makes this complicated.

As far as I know if you applied for a business visa for company A and then you want to work for company B you have to leave the country (i.e. to Cambodia) and apply for a new visa. And obviously be careful that you have all the documents from company B when you do that...