problems renewing/upgrading mobile & contract

I have spent two weeks trying to renew my contract and upgrade my mobile phone. I have been cut off numerous times either mid-sentence, when holding to be put through to yet another colleague or for an initial answer to my call. I have been promised phone calls that don't happen. I was even given a number to call which proved to be for Carphone Warehouse who then put me through to a TalkTalk operative. I have sent numerous e-mails but instead of an e-mail response they call and leave messages with phone numbers where I cannot get an answer, or they call and I get cut off mid-sentence while trying to ascertain the information I need. The customer service has been abysmal. As my mobile contact ends in 3 days I have had to go ahead with an order on line without being able to talk to someone as I had wanted. The broadband service is just about acceptable but variable and is unavailable or slow on a regular basis.