Car track selling false information not happy at all

We app**** for tracker in 2020, my husband was advised with the amount that is the premium, and they advised also the will be a pro data amount to be paid, that we agreed, later on after car was installed with tracking someone from the company called and advised with a different amount, this has been going on and being harrased to pay an amount that was not agreed on, we demanded an account Manger to sort issue out without fail u till today we still being called daily, but without resolving the problem