Nissan SA - bad customer service and bad stock planning/availability

Nissan South Africa don't carry crucial wear and tear stock items and I have had to wait since the 17th of October for a part to be sourced. They refused to accept this responsibility as their own and made no effort to accomodate me with a replacement vehicle. The call centre refuses to let me speak to a senior manager for Customer Services and hence the query only goes as far as the call centre. I have been heavily inconvenienced during this time, with no use of my vehicle. I am incurring costs of finance and insurance on an item which I am not getting the use of. Nissan have have completely discarded of best practice and good customer service.