After accident – insurance from the accident opponent pays too little ?!

Hello! Had an accident about 3 weeks ago – I parked normally in a parking lot and the cause of the accident drove me in obliquely in the back. Was not even on site – I happened to come out about half an hour later and he even waited, was very nice and insightful. Then changed everything necessary. In my contract workshop (Toyota) I had a cost estimate created. In this case the damage is estimated at 1,399, including VAT. I have not yet had the damage repaired – suppose that I would have done it, which must be the result of the opposing insurance, I would have had to pay almost half alone now. Is the procedure of the insurance so correct? Can I challenge this? We had not brought the police to it at the time, since they did not have any damage to the sheet metal. What possibilities do I have now ? =/