The people at IFA are probably not the actual tuya decision makers, and whatever they said got wiped off the table by some higher up at Tuya. Which makes sense, since now from the perspective of Tuya, Athom is just LG. This means your name got elevated to different discussion tables in tuya and probably got more scrutinty from the business/finance/strategy folks.
Since Athom does not want to go for the Tuya offered solution, what routes/ options are you exploring or willing to explore? Or are you waiting for Tuya to change their decision?
Because if you are only doing the latter, i think expectations are not fairly managed here.
What would help is clear communication on the value for Athom to offer a Tuya integration. Are you willing to work for it? Invest for it? Have hassle for it?
Or is this only feature you want to support it it comes easy?
At this point in time we know:
Athom becomes LG
Tuya did something that was not agreed upon with Athom (but maybe with LG?)
Tuya offers solution that requires investment from Athom. ( is it actually a better (technical) solution in the long term, apart from the work you would have to do or investments to make?)
Athom refuses the proposed solution
Have you considered asking your users for a contribution for the tuya app? I would be more than happy to pay a fee, will be way cheaper than swapping out AC units, underfloor heaters , leds strips and switching sockets and be simpler than having to have two apps to control things and not having to explain that to my family…
If you are 16 and need some bolts for a project, the hardware store will probably give them for free ( because they like kids learning that stuff), if that same kid is now 26 and works for Eriks, that same bolt will cost a premium and everyone understands that. How homey/Athom fits in this story is for you to decide 
