Unknown phone credit

Good day

My name is Alina Ramalope , I have been receiving calls from Nashua mobile claiming that I have an account with them and I am in debt , I have never opened a Nashua account for any contract , I told them this from the beginning but they are still calling me and telling me they are taking me to debt collectors . They told me I owe them ~R3500, please assist me on this matter.

Kind Regards,

Alina Ramalope