O2 against me. I would like to pay the cost of the iPhone aroun 700- 800 pounds. O2 claim 1200 pounds .

I received a iPhone from mobile phone direct, the agreement was 150Gb with O2 provider. O2 sent me SIM which doesn't work. I contact O2, I complain,I chat with O2 but the SIM card doesn't work.In 3 month but they keep send me bills. I don't pay. The final bill is 1200 pounds,but the iPhone cost 700- 800. Because of this I lose some jobs and loss of earnings. I would like to pay the cost of the iPhone, and nothing else. I got county court in May. How can I set my defense. Thanks you.