Netstar

I'm having terrifying experience with Netstar they installed faulty unit in my car I reported the matter within 5 days after installation they contacted me after 11 days after I've sent them tons of emails and when I want to cancel the policy they referring to the terms and conditions of which were not brought up to my attention, I tried to check the emails that they've send when I took policy they show error message when I open them, please help me with this matter