Misleading service

I received a call in March this year from a lady saying that they're phoning from Telkom. She asked to please update our details on the form that she sent. I just ignored the email as I had no time for that. A couple of days late she phoned again asking for the form, which I've ignored again, after the 3rd or 4th time I filled in the form just to get this woman off my back. I was told this was to update our contact details. 3 months down the line, I get a call from Simone Naidoo requesting payment. Of course I had no idea what she was talking about, I didn't receive an invoice a quote or any further corresponds with regards to this. To my big surprise, she then sent me an invoice for R9540.00. After receiving this invoice I tried to phone them back but you can't get hold of them at all and they're not responding to any emails. I told Simone that I was not the authorized person to sign for this and that I was told this is strictly to update details with no cost involved. Her response was, "Well I signed for this so I'm liable for payment". The cancellation is also *******, you need to cancel within 5 days, and pay a cancellation fee of R4000.00+. I then asked her why should I pay for a service that hasn't been done. She then sent me a link to whiteonlinepages.co.za with our company details and brief description of our company. We did not provide them with this information as to what our company does etc. After this I've been getting calls weekly demanding money. I refuse to pay them but don't know how to get these people off my back. Please can someone advise on what do to in this scenario?