Very bad customer care and unreasonable

On about December I registered a claim for my car. Around jan all the assessments and so forth was done claim was approved by 18th or so of january. By then i was using the 30 days courtesy car from the insurer. Up until this point there car hasnt recieved parts so that it can be fixed and im paying for the car thats standstill. I contacted denise and tiffany they are adamant that its not their problem that the parts are delayed and my rental has expired. However, i contacted other dealers and mercedes benz that confirmed they would have had parts for my car withing a reasonable time a week at some instance. I made the insurer aware , a consultation male said he will make sure that he will make sure he copy me in an email that will allow the insurer to pay me in cash so i can take my car where there will be a reasonable time to fix my car. That did not happen. I spoke to denise and tiffany on friday 17/02/2023 and she said to me a gentleman confirmed that i chose that renew it sandton should be there preferred service provider and i agreed to it she said she will provide recording till today that has not been done and actually today she says there is nothing that they can do as its not their fault but my argument is that its not my fault either and they solely chose a provider of their choice with no consultation done with me as advised by Mr Collen. I dont have a courtesy car nor do i have a car and im paying for a car thats not being given priority. I requested that they may give me my car and i go fix it where i want and any workmanship becomes my liability they dont want at the same time they dont want to extend my car rental. You can not fault me on delays that are happening because of who you chose to work with without my input or any engagement with the provider when i have providers that would have been done with my car now. You should do better