Vox Telecom fibre billed me for Cell C line usage

Vox Fibre were notified of a requirement of a new fibre line installation as part of their March 2019 promotion. Instead of installing a new free line as advertised, they incorrectly reallocated my existing Cell c fibre line to Vox and billed me for using my own cellC fibre. When requested a refund for their error they ignored my request saying I don't have email proof as it was communicated telephonically and they cant find any recording of any such instruction.