Hello Malsiluk and
to the forums.
I am not sure what is the best way to go.
What area do you live in? as there could be someone who works in that franchise that could help you. I hope you have asked that you are refunded the costs for teh TV programs you can't watch due to the STB being replaced and being unable to activate. The fact they cannot activate the STB isn't your fault it's NTLs. If they had repaired the fault then it would work so thay shouldn't be allowed to charge for a service you cannot receive.