I had that problem when I tried bt mobile. You'll have to keep badgering them to sort it out their end
Had another webchat with them today for over an hour, where they asked me to complete the steps i told them at the start i had already done
they then told me that "there is a fault in your area, please call us back in 3 days"
when i informed the guy i traveled over 100 miles with the phone yesterday and didnt get data once he said that the fault was affecting that area too (despite me not telling him where i went)
in the end he caved and ordered a replacement SIM, which should be here by thursday