Telkom ****** me

I had a rep come to my house and Install the telkom Fibre line which I do a cash payment for and then out of the blue they invoice r1330 for a r315 service when I tried ro query this many times I was told they do not know why so I canceled my services with telkom now they are harassing me saying I signed a contract and I have to pay weather I use the service or not but I have nor signed any agreement wat so ever with telkom very disappointed