Phone sold with software problems

Firstly I purchased a sony experia z2 from this store. As per the sales man that is. Upon reviewing android versions and researching the serial number i found this was actually the z1. Now the phone has a problem with the software or something as when i use it the screen becomes unresponsive or the menu gets stuck between 2 pages. It heats up extremely and then bombs out. Is this the type of service the public can expect from cadh converters? They are refusing to give me a refund saying the have to send it for repairs. I do not want a phone that is already giving me problems after one week and an older model that i believed i purchased. This is unacceptable.