Catrack harrasing me

I contacted Catrack on the 10th of March requesting a tracking unit for my car. I gave all my details and approved a Debicheck Mandate as well. Someone was supposed to call me to arrange installation but instead they have been harrasing me ever since, calling me then when I answer no one speaks they are just breathing, they do this multiple times a day. I still haven't gotten much unit installed. I made the worst decision by choosing Catrack. Cancelled the Debicheck Mandate, so they can forget about getting money from me, now they must just stop calling me😡