xz2c (xz2) wont book into any mobile network

Hi,

my brand new xz2c doesnt book into any of the available local mobile networks. It only detects the network as 2G but I know I have full 4G coverage here (!&&* the cell tower is right across the street!). Problem is I only found this out after I had already unlocked the bootloader so now the support company refused a repair/exchange. But they DID officially confirm the issue at least, happening on latest stock image/firmware (and LineageOS too). Anything I can do here or is that thing now a wifi-only “phone”?