Nashua Mobile phone contract

I get an sms stating i owe R11k odd for a Nashua amobile aaccount. They have not called me to send me or show me where i signed for this so called phone contract yet now i must pay to prevent legal action. I called their HQ was holding for 6mins and line disconnected. Just another tactic to make as if i have not made contact with them. What rights do i have as a consumer to prevent my name being dragged through the mud and prevent my name getting blacklisted. This is just not ethical. Nashua Mobile closed down many years ago why call me and not have any proof that i did indeed sign. With all the fruad on peoples IDs how can this be me if i never had a contract with this people???? What can i do