Not happy with the service, they are only telling me now that I have to pay 460 for the backup unit that was installed with the tracker to my car

Not happy with the service, they are only telling me now that I have to pay 460 for the backup unit that was installed with the tracker to my car. They told me that they have made a mistake, but now they have rectified that. Initial, they never told me that there such problem that I should be aware off. So where will I get that extra money to pay their mistake. The person who made that mistake like they have said it’s their mistake, must be accountable for that. Not the clients.