Harrassment from DSTV

I have people claiming to be of DSTV multi choice busy harassing me almost everyday, they don't say whatever they need to say immediately when I say I don't have an account with Multi choice they drop the call. Now my question is why am I getting harassed like this now they even call on my landline number which I find it disturbing because I never gave them the numbers. My question is how can you owe a prepaid service if that's the reasons the are calling? DStv is a problem in my life the fact that I cancelled their services I don't regret even a single day been four years now and they have turned to be a burden in my life harassing me every week..