I wouldn't go trying to sign up anywhere else yet, a mobile is about the easiest check to pass so they could be meaning something else (like wrong bank details or something not specifically credit check related but that causes their system to say no) and whatever issue O2 have got with you at carphone will be the same at P4U.
You need to get that fixed or you could end up trashing your credit file, ever check gets registered even if you fail.
You need to get that fixed or you could end up trashing your credit file, ever check gets registered even if you fail.