#refusal to honour T & C of OEM Warranty clause

Shocking service from Nissan SA. We changed the tyre/s on my son's vehicle and when taking the wheels off, Tiger Wheel and Tyre highlighted us to a bolt that had stripped. The vehicle is only 2 years old with less than 30 000 km on the odo. The only people that have ever worked on my vehicle are Nissan approved workshops, specifically Nissan Northcliff who is subsequently closed down. We took the vehicle to Nissan Randburg who then advised us that the drum is also damaged. The only person/s that could have caused any damage to the vehicle is Nissan Northcliff as they are the only workshop that has worked on my son's vehicle. I have been escalating this matter since December and cannot get a supervisor and/or managed to call me back. They have now come back and said that there is inconclusive evidence as to what caused the damage. I then asked them how did these components get damaged as I now sit with this and have already paid out R 1500 to get the damaged bolt fixed. The vehicle is still within its OEM service plan and warranty. Whilst the component may not be covered, defective workmanship is as long as certain criteria is adhered to which we have done. They keep pushing back to Tiger Wheel and Tyre who highlighted us to the issue when taking the tyre OFF not putting it back. Nissan Randburg confirmed the damage to the drum. They REFUSE to acknowledge that one of their approved OEM workshops damaged my vehicle and REFUSE to honour their defective workmanship clause within the OEM Warranty wording. Typical, all lip service and no action. I have to continually follow up and chase this only to have them negate their responsiblity. Their managers have not been available since December? How do you run a business in this manner!