10 day old phone faulty

On the 29-08-2015 I renewed my Cell C contract with a Microsoft 640LTE Lumia phone. I was informed that should the handset give me problem, I must contact the help 140 or if it damaged return the unit within 7 days.<br> On the 3rd of September I experienced a problem, when people contacted me the call would either drop or sometimes if I answered they caller could hear me. I sent an email to the customer support centre explaining the proble. Nomsa Sithole returned my call, but of course could not assist as the I could not answer her. On the 4th I called the call centre and was informed that the call had been resolved and closed. The following day the phone started working due to some miracle. Today the problem reoccurred. I took the unit into Cell C in Pinetown, I was informed that even though the unit was 11 days old they would have to send it in for repairs. They had no loan units available. I've been a client for 8 years. I feel the unit should have been swapped. Had Cell C followed up on the call properly and investigated I would be happy instead I'm bitterly dissappointed.<br> Regards Russell