keep on harrassing

The company above keep phoning me on my cell. The want to speak to my husband and not me, but its my cell number. When he is speaking, they start telling him he is that person, he has given his ID no. but still they said he's lying. They send sms's and said they will start legal action. I've asked them and they said it is for an account in December 2010? We've contacted our medical aid and they confirm there was no such incident. They've got an attitude and are very rude over the phone when you say that you're not the person they looking for? We're now really fed-up with these company. each and every weak they phone from different numbers and are sending a sms. please, what can we do? WE are not the only people that's surname is Du Plessis?