Alarm or mobilizer not working

Hello and welcome to 2CarPros.

Your description sounds like you have either a failed remote, or the receiver in the vehicle has failed. This vehicle doesn't have a back-up mechanical key?
The first step would be to test the remote. However, not many places have testing gear, the dealer may be the only one available. If the remote tests okay then the next step involves connecting the vehicle to a scan tool and verifying that the receiver is or is not getting the signal and if it reads it correctly. Unfortunately the security system in most vehicles are designed to prevent people from testing them to prevent the system from being tampered with unless you have the proper tools.