****ty tracking institution (car track)

I sold my car last year September since then I've been trying to cancel my contract, when I call they would tell me that I'm with Ctrack or sometimes they would put me on hold until I run out of airtime. It was a bit difficult for me because I was out of the country, they would send me messages to say my device was tested and it's working properly which clearly shows that someone is not doing job, only in July they finally decided to reply and sent me a confirmation of cancelation, for 10 months I've been paying for something that I don't own anymore and today car track has got the nerve to send me an sms stating that I must not forget to pay 725 for what? Car track is full of ****!