I posted elsewhere by mistake, however my situation pretty much belongs here.

Newcomer in forums as well.

To get to the point, before reentering Cambodia from Thailand, I applied for a new passport in Bangkok. After a fortnight I was notified that my new passport is ready for pickup so I left Cambodia in order to collect it from Bangkok and get back to Cambodia again.

At the borders (Poipet) I presented both passports with the Thai exit stamp in the old one. The Thai officer asked for some additional docs given by the embassy in similar circumstances and he also mentioned that the embassy officials should have canceled my old passport when I received the new one, which unfortunately wasn't the case. To cut things short, they let me pass by stamping my old passport so I entered Cambodia with the same passport which expires in October.

I contacted my embassy in Bangkok and they advised me to go in the local immigration office in Cambodia to pass the Cambodian entry stamp in my new passport.

In about 10 days from now I am planning to leave Cambodia for good and go back to Thailand on a tourist visa as well, however I'm still worrying. What if things don't go as expected in Poipet?

Thanks in advance for any info.

Suggest you follow the advise given by your Embassy !

I went to the local police station (Krong Preah Vihear) and they told me to go to an airport (Phnom Penh or Siem Reap) to get this overwith. I am sure there must be some department to deal with similar immigration situations but the officers here didnt know anything about it.