Miele demanding payment for a part they never delivered to me

In September 2018 I asked Miele (Pty) Ltd if they could supply an extra oven rack for my Miele stove. They said it would have to be delivered from Germany and then I never heard from Miele again about this until I got an invoice in November 2019 for the oven rack. I never received the rack. When I asked for proof of receipt, Victor from Miele sent me two worksheets for work Miele said they had done for me. One was for work they had done and which I had paid for, the other was for delivery of the oven rack. The customer signatures on the two worksheets are quite different. I pointed this out to Victor and told him that the signature on the oven rack worksheet is not mine. I also sent him an email confirming this. Despite this, in February 2020 Miele has now handed over this account to lawyers. It is absolutely shocking that Miele is demanding payment for a part they never delivered to me. I know I did not receive the oven rack. Miele is unable to provide any proof that they delivered it to me. It seems that Miele's strategy is to harass me, so that I will in desperation pay for the part, even though I never received it. What an awful company.