REGRET BUYING A SONY XPERIA Z3

PLEASE, I'm experiencing serious problems with my XPERIA Z3 which we bought on the 3 August 2015 form MTN Summit Road in Sandton. The phone stopped working in September 2015. I took the phone back to MTN. The phone can not seem to connect to the NETWORK at all and it showed flight mode that needed to be turned off, and mean while flight mode was off. On taking the phone to MTN they advised me that the phone was \beyond economical repair"i asked for a reason coz there was nothing wrong with the phone"