To be fair to Immigration in Chiang Mai they probably have very little guidance about the DTV. It is not an Immigration Department Visa - it is MFA. I read one post on here where someone claimed they had the DTV cancelled in Thailand through an agency - no doubt it included a service fee. There are other reports that only the issuing authority can cancel ie MFA and then only where it was issued - in your case Cambodia. Good luck with it. It took me 2 trips to Singapore to get a "B" from an "O". Hope you get yours sorted without too much hassle.
If buying new the dealer should do everything for you. If 2nd hand you need a Certificate of Residence to transfer the Green Book (Ownership book) to you. It is all done at the Department of land Transport. Same place you pay the tax and basic insurance
I was back in UK when it first shown. Then my pal bought the DVD's - used to watch with sub-titles so caught all the jokes missed when just listening :-)
Anonymous participant Multi Entry Tourist Visa. It is for 6 months and can enter multiple times. 60 days per entry and extend 30 days (Subject to discretion of office of course)
Anonymous participant I think you need to try and find out why Cambodia rejected you and what they put as the reason. I am just speculating here but it looks like Vietnam took one look at your record and refused without even assessing it! Maybe get a METV to cover for 6 months and apply again?