Android TV box MAC address keeps changing

I had a MAC address when I was using IPTV on my Android TV box in Turkey. Since I've returned to the UK and plugged it in here, the MAC address keeps changing, and now I can no longer access my IPTV service as it's tied to the other MAC address. The supplier wants me to change my MAC address back, but I can't find any way that actually works. Why would my MAC address keep changing?