Motherboard was stolen in Apple Repair Store in Beijing

Hi, I am newbie in this forum. I am living in Guilin, China now. About two months ago, my Macbook air suddenly died, it doesn't work any more. So, I brought it to a local Apple authorized store to repair it, the local store owner said they are not capable of repairing it, but they can send it to an Apple repair store in Beijing, China to repair it. The guys in the Apple repair store in Beijing will check it and give me a price quote before they get my permission to repair it. If I disagree, I will just pay the shipping fee and get my computer back. It sounds reasonable, so I let the local store owner send my Macbook Air to the Apple repair store in Beijing. After about 3 weeks, the local store owner called me and said the guys in Beijing checked it and found the motherboard was flooded and needs to be replaced. But I didn't believe it since my computer has never been flooded, so I said I didn't want my computer to be repaired, please just send my computer back. After another two weeks, I went to the local Apple authorized store to pick up my computer. However, after I opened the backcover of the computer in the store, I found my original motherboard was stolen, it was replaced with a crapy flooded motherboard, because the markers I made on the motherboard disappeared. Actually, before I gave them my computer, I scratched some markers with knife on the motherboard and took some pictures. I told the store owner it’s not my original motherboard, and he agreed after comparing it with the pictures that I took before. Then he sent the computer back to Beijing, and also sent the pictures to ask them to check what happened. After another two weeks, I got call to pick up my computer in the local Apple authorized store. But, I found this time they just forged the markers according to the pictures sent to them. They didn't know actually I didn't give them all the pictures of the markers, so I can not find other markers that I made. I told them I am 100 percent sure it is not my original motherboard, but the guys in the Apple repair store in Beijing denied it. Please let me know with whom I should contact to get my original motherboard back? I have searched the whole website of Apple, I couldn't find any email I can shoot, it is very frustrating.