Cancelled account - still receiving invoices - no customer care

We have cancelled our Telkom Business Account in February 2018. Subsequently we are still receiving invoices. I have been trying to call Telkom, but we do not have a Telkom line anymore and moved over to VOIP telephones. We are not able to get through to the call center number from a VOIP phone. I have searched their website and Facebook and can not get any other number to call. Today we received a letter of demand for the account we closed. I am shocked and frustrated because I have been contacting Telkom via email and Facebook almost weekly. In the letter Telkom states "we urge you to contact our offices without delay", but they don't list their contact details in the letter? Shocking. I have been sending emails and Facebook-messenger messages since February 2018 and the problem is not being resolved. All I want is for someone at Telkom to respond to my my messages, for the invoices to be reversed, an updated statement to be sent to me, is that too much to ask? Shocking service.