Initial prompt response, thereafter no more joy.

I initially had a prompt response from complaint department, but have not recieved much help or gained a resolution to my device issue. My Cat s50 was returned from it's 3rd repair today. It now has an additional fault which I never even experienced, I can't use this device and have had almost no use from it.<br> <br> How am expected to pay for this monthly??? Where do I get answers as trying to from the shop is useless??? I am at a loss but must still pay.<br> <br>