Bad service for AA Warranties

I am a paid member, my vehicle had a mechanical problem on the gearbox, I send it in the the mechanical workshop where they did a diagnostic report witch the result is that they will need to open and replace a part. All documentation was send to AA and they send also a assessor to investigate. After the repair AA decided that they will not pay me one sent. There reason is that I send the vehicle to the mechanical shop before the assessor see the vehicle. But he said that I need to send the vehicle to a registered mechanic workshop.so for me I cant see that he will be able to see inside the gearbox if it was not opened. he saw the part and all the documents as requested. And still he decided to pay me nothing. Why do we have assurance if they refuse to pay. Very bad service from AA Warranties a Lombard Insurance Company Limited