Fabia 1 2005 Key remote locking problems

Hi everyone,

I have read through many of  the posts on here to resolve remote key locking problem... unfortunately I still have an issue. Where I am in the process:

-  2 keys, remote locking on one key works fine. The other key used to work and now only manually locks/unlocks

- I have replaced the key battery and the red LED flashes when you push the open or lock buttons

- I have tried pairing the key that isnt working - ignition on and key in the drivers door method that is described on here - the car did not beep or flash the indicators

My guess is the radio transponder has given up. Before buying one I wanted to know if there is anything else I can try. Any thoughts?

Thank you!