Simple, easiest things first. Have you looked for a channel change set of dip switches.

On the Hand set it is often found in the battery compartment. Flip a couple, make the switches on the receiver match.

Rolling codes have a little "slop" built in to allow for accidental pressing of the remote when your not home. I think it's some thing like +/- 10ish. One or the other of you either needs to totally reset the sequence or advance your code about by operating the remotes 100 times. You can do it with just the remote of prem then re-sync it with the receiver. I assuming only one remote has this problem. I vote for finding how to do a total reset and resync