Poor servive

I have lodged a claim on the 23 April 2019 and still have not got my vehicle repaired. The service is poor. My car was damaged by a pothole, the mag wheel tyre (Rim) was damaged and need to be replaced. Did a quotation of the Rim at Mercedes and emailed everything. They told me the claim was approved all but they do not deal with Mercedes when it comes to tyres and rims. Told them im going to pay for my Rim and they must refund me back. The consultant told me they do not deposit money to clients only direct to the service providers. Im trying to resolve the issue but they are not helping. Mercedes only accept full payment when buying parts. Now im caught up in the middle I do not have a car for the whole month. Then I gave them all the relevant information and the people that they can talk at Mercedes regarding how this matter of payment can be resolved but no feedback and they are simply not responding to emails im sending nothing at all. The service is poor and heartbreaking if they cannot refund me for paying the rim myself because they do not do payment to their clients what im a supposed to do. So im doing their work trying to find solution to the problem but they are not helping.