I have dumped 4 one-tel accounts since they were taken over by Talk Talk.
Customer service is just awful: you can be on hold waiting for an operator for 10 mins then they just say 'nobody's available, leave a message, we'll get back to you in 48 hours', but then nobody calls you.
I've also been double billed but it took a month to actually get through to someone to correct it, about 20 emails and calls.
Their low cost *really* isn't worth the hassle (in my opinion!)
BW