Be careful of Aliexpress and Alibaba

I ordered 2 items and was provided with 2 tracking numbers. The items were never received. According to them they were delivered to the Post Office. I never received them Post Office does not respond Aliexpress advertise a money back guarantee that you will receive your order. My claim and appeal was rejected as such:Since you didn't provide valid official document to prove that you didn't receive the package, we feel sorry that your claim cannot be supported" How do you provide document proof that you did NOT receive it