They can't use people who speak "the Queen's English" because nobody uses Received Pronunciation.
But the real reason is that because the broadband is provided so cheaply Carphone Warehouse have to make savings elsewhere, which involves siting their call centres in the Indian Sub-Continent. Now if you could speak Gujarati or Hindi as well as they call centre staff can speak English then I would understand your complaint.
As for Talk Talk tech support, did you get a call reference? Call back and persist with the music, give them the call ref and tell the operative that your call hasn't been resolved, they should then pass you back to the UK tech support, who offer a very good and knowledgeable service. This person should also call you back if you express concern over the mounting cost of the call.