Do not sign up, you won't be able to cancel

I started using Netstar tracker ever since I bought my car in 2014 they called in 2018 saying I need to upgrade my tracker because the 1 I am using is old and it will be difficult to recover my car should it get lost. They came installed they new device, last year I called Netstar to downgrade my package wanting to pay less than what I am paying as it is too much for me. I was told I cannot downgrade but can only upgrade then I told them I want to cancel my contract, they said I cannot cancel my contract as I am on a 18 month contract I told them I need a contract or voice recording where I agreed to the 18 months, I am still waiting. Today I received an email of the increase, I call and ask to cancel my contract again they say I am on 36 months contract, I asked again for where I signed for the 36 months contract I am still waiting