.
I tested the key fob it's sending the signal at correct frequency with each press of any of the buttons.
The issue is that when I switch off the engine and take the key out I press a button and it will work, but if I press again and again and keep pressing nothing is happening with the car like the signal is not received. When I put the key back in the socked and start the engine then switch is off take out the key it will work again but ONCE only, so only 1 press of a button. Anyone else had similar problem?

 

Battery in fob needs replacement.

 

Thank you but I bought a frequency tester and the key keeps sending the signal each time I press a button

 

Have you checked the splice for the antenna ground? Passenger side, front door, in that large loom under the sill trim. If you've ever had the sunroof drains blocked/degraded/torn, it can corrode and cause the issue you're talking about.