how do i fix my 1.2 renault clio 2003 key fob?

hi, so i need help about my key fob, i have a renault clio 2003. I used the key and car yesterday with no problem, went to use the key this morning the key button would not work to open or lock the car. The red light on the key is no longer working so i instantly thought it was the battery so iv changed it, yet nothing working again.
iv had to open it manually on the passenger side and climb through but once in iv opened the drivers side and it opens the rest of the car doors? what is wrong with it? need help, hoping its not the central locking itself :( thank you in advance.