Huawei Offers Free Engraving, But We Can't Give It To You

So basically I saw an article stating that you receive a free huawei back cover engraving of your choice offered by huawei provided that you buy one of their premium phones eg. Huawei Mate 10,P10,P10 Plus,P20, P20 Pro and so forth.. Upon discovering this, I was excited as a puppy because now I can personalize my my huawei smartphone, little did I know that I was in for a shock, as I spoke to two of their customer care agents, one said I can engrave on my Mate 10 Pro, the other said I couldn't because it's not covered by the free service, I sent him proof from various sources including the huawei official page only to be told that my phone has a glass back cover so I couldn't, I asked him about engraving on the p20, he said its possible, what I don't understand is why can't they engrave on mine because it's the same back cover they use on the p20 and p20 pro, it's made of glass, not plastic.. Then later today Nadia, I forgot her surname told me that I can't engrave on the mate 10 or the p20 because apperantly the laser burns the glass and it cracks it for some odd reason, what I want to know is why are you offering a service that you can not provide your customers with? It's like saying your huawei phones have supercharge but you don't have any stock of the supercharge batteries or charger to begin with... I would like to receive clarity.. Iv been a loyal Huawei customer since the first p8 was released but the service is really terrible, appalling to be exact.