double payment of damage to liability

Hello dear readers! I hope you can give me concrete help or clarify the situation. At the beginning of 2009 we had a liability damage as a victim (evil parked out, drove to our car). Now the whole “thing” ran a little curious… The vehicle was presented to the Wekstatt, cost estimate, next expert report. The opposing insurance provided us with a calculation check (not quite equal to the estimate – this was before the assessment The AH claimed the balance of the total repair costs from the opposing insurance. The insurance then paid again the total amount of the repair. Clearly formulated – the damage was paid almost twice by the opposing insurance. [Probably the apprentice was used to regulate the costs] The AH has the excess amount of the AH. of course, you have to pay us back. Now my question(s): 1. Until when does the insurance company have the possibility to recover the too much paid? 2. Is it necessary to report the overpayment (enrichment) yourself? 3. Other information? Thank you very much in advance.