Why should I pay excess while I am a third party??

I had an accident on R80 (Mabopane highway) whereby a car hit mine from behind. The party involved was at fault and he contacted his insurance company, Auto and General, which I am also insured with. The consultant asked him to pass the phone to me, which he did, and then we discussed the incident. We were both advised to make a statement at the police station, and so did we, with ther other party admiting his guilt on the matter. I contacted Auto and General and furnished them with all the details. The consultant informed me that I'd have to pay excess of R11, 000.00. I refused and clarified that I am a third party in this whole thing, and that I was calling to inform them of my side of the story. We reached an agreement that she will contact the other party and proceed with the claim from the other side. After a few days, I was contacted by the repair shop and was informed that my car was booked in for repairs. There was no further communication between I and Auto and General - it is in their nature not to communicate, I thought to myself. Finally, the car was ready for collection and to my surprise they wanted R11,000.00 before I collect the car. I then contacted Auto and General to enquire following the conversation we had regarding the excess. I tried and tried to get hold of them and when I finally did, the lady insisted that I had yo pay the R11k, and that I should have never claimed on my side. How was I to know that I shouldn't contact my insurance during such incidents? Did I not mention that I was hit from behind and that the other party was wrong and he admits it? Did he not claim? And most of all, did Auto and General inform me that I MUST pay the excess regardless of what happens? What kind of insurance company does this to their clients? Furthermore, they say I must pay the fee and they will refund once they have some discussion on their side. What pains more is that I and the guilty party are both insured by the same company. The company that plays hide and seek. I am writing this hoping to get this issue sorted, and if this is truly a reputable company, it would definately sort this out ASAP. I cant struggle this much while I am the third party in this whole scenario. I need my car back.