Dear Khun Suvitcha,
I see your points but we have signed a contract and we rely on our counsel advices and opinion as we’re not familiar with all the tax issues in Thailand, this is why I have offered repeatedly yesterday to have a 3 way call with you, and other party from Irradiance if you desire so as well as our counsel to settle this issues, and I find it more effective to have a live conversation where all issues can be settled and agreed at once or mitigated. 
It’s crystal clear as per the agreement that in no case we are to be subjected to paying VAT twice on the same imported equipment, so let me know if you want to have a call or not and what is your availability.
Best