I am trying to sell a in California. The one next to me and mine were brought at the same time. The decal numbers got mixed up. We got next door's decal number. Now we are trying to fix this mess and have had no luck. Is there any advice that anyone can give me? Is there any way that I can get a new decal number?

Have you been to the licensing department, what have you done so far to try and fix it

Suggest you and your neighbor take whatever documents you have to prove ownership of your homes and the decal information and go in person to the agency who issued the decals and speak to them in person. Chances are slim and none this can be resolved on the phone without the agency seeing documentation in their office to make copies of.