Pathetic MTN service to clear misallocated debt against my name

When applying for a bond recently I was told by the credit agency they use that I have outstanding debt with MTN and hence my application was declined. On investigating further with them the debt I have accrued is on a number I don't own nor have I ever used that number even though it is listed against my ID number. When I try get hold of their legal department (via email or call), no one responds. No one seems to know what is going on there and I refuse to pay a bill that I do not own. The longer this takes, the longer I cannot apply for my bond (or any loan for that matter) and MTN's service is absolutely pathetic!