Hi I had a similar problem... you need to replace the circuit board for the gearing, in this image below you will see 2 little metal clicky buttons these get flattened due to excessive power gearing up and down and eventually stop working.. buy a new circuit board on ebay or similar and follow a guide on youtube how to replace and it should all work again.. or buy a shifter for G29 or remap your gears to different buttons but that defeats the purpose of the paddles...
Good luck with it