Debt problem

I am very disappointed in Chubb, we had an alarm at home and my dad was responsible for it but then he passed away in 2014 and we reported that with Chubb that they must stop everything cause we cannot afford it anymore and they came to remove the alarm but funny part is sumbody came from Chubb told us to sign a contract for that alarm and I did and now I keep on getting statements that I myself took over the alarm and now am owing R4200 and for which alarm I don't know cause we don't have an alarm at home anymore Chubb came 2remove it but am very angry and disappointed cause they ruining my name with this debt and if I have to take more steps further I will if they don't solve this matter, cause when I call Chubb they don't give me a straight answer they keep on saying they will get back to me they still checking the matter but am not getting any responds I even faxed them the contract to show that the alarm was removed but still nothing. Even if I wanted an alarm again I wouldn't take Chubb again after this thing that is happening