Selling cell phones without all information and across border restrictions

For 6 years I have been an cellular contract holder of 5 devices. Upgrade 4 of the devices the 11th December 2021. The 2 Huawei nova 8i device I found out is not compatible in USA and some other countries I work in rendering it useless to me. The 12th December I went back to ask if they could change devices since none of their employees informed me of this issue and nowhere in their contracts is this problem even been mentioned.. I didn't want to move to an cheaper contract, but just change to Samsung A52. An device change that is excepted in other countries when buying network cards. Yet after an week and me having the devices still in their boxes as issued to me by telkom they refuse to exchange. The sales person opened the boxes to check devices, now they tell me because its open they can't change devices. This is bull and I now will refuse to let this go until the matter gets settled. *********** management that can't see reason and unwillingness to help