OP- take any residency/lease papers you may have too as this will substantiate where you live. If you happen to have a helpful landlord, it might save a lot of hassle in communication/verifying your residency if he/she went along with you. They will know where the local sangkat is.

A lot of this will depend on the attitude of your local sangkat. I say all this coz I've heard on expat forums and FB groups and personal experience that my local sangkat has turned expats away with various excuses and/or asked for money. Even one of Mrs Cargo's khmer friends got turned away by this sangkat saying she needed to bring her landlord. Others suggest to seek assistance from the sangkat village chief (Phum head?) but this is not easy to find out who it is and how to contact (@timmydownawell can add info).

Hopefully, this won't be necessary in your instance but just giving you a heads up about it. Good luck.