Blacklist

I recently canceled with service with cartrack. They notice me I need to pay the cancelation fee. My made an agreement that I pay a cent amount tell I finsh the cancelation fee. I have paying that amount every single months. Yesterday they I called me that I need to the pay the balance or they'll have to put on under blacklist. I told that I don't have money to pay the balance , and I will pay until I finished. Today I received a email from that cartrack that I under blacklist. I have that stroke, not well and I will keep continuing pay. How is, I have be paying? But I under blacklist.