Regulatory period Car casco damage / theft ?

Hello together, about 5 weeks ago my car was stolen at night from the road. Telephone damage report with the insurance as well as pol. display was made directly on the night morning. All required documents, damage report, car keys, copies of letter and bill as well as all invoices and contracts in the original sent to the insurance. Also the cancellation confirmation. The 4 week waiting period has now elapsed for a few days. In the same way, the prosecutor’s letter that the investigation procedure was terminated unsuccessfully. Now I have run out of data, which I can now expect to have a quick refund of the time value. This does not seem to be the case. The insurance company would like to carry out its own investigations, for example, to have the car keys examined (which it has had for 5 weeks) and the devil knows what else. I understand that an insurance company has to secure itself. My question is, is this procedure of insurance common and correct and I am only sensitive or really want to gain time ? What experiences have others made ? Is it worth it to resist it and if so how or is it rather counterproductive ? Many thanks to those who take the time to answer me. Greetings from B Thomas