Dispute over the guarantee

Hello together, bought a car in mid-February (A5) and after about 4-5 weeks the exhaust control light went on – Audiwerkstatt found faults and gave me an estimate of about 1000€. I paid 170€ for the visit. I bought it from the car dealer and have a normal purchase contract. My car dealer said he did not know if he agreed to mail him the estimate. Now for 2 weeks he doesn’t answer, does not answer the phone, etc. What should I do? Go to the lawyer? Consumer protection center or similar? Get car repaired, or wait? I hope it won’t get worse, it can happen that e.g. the DPF filter clogs up. Then the costs increase. Thank you for your help, Sebastian P.S. I hope this is the right place in the forum to post the topic.