Separate Rental Insurance - 3rd Party Cover

Does anyone know what the position is re 3rd party damage. I had a minor incident which left little damage to the rental vehicle but approx £1000 of damage to the 3rd party. The excess is £1250.

I purchased a separate Halo/Zurich CDW policy through icarhireinsurance and they now tell me that they dont cover 3rd party claims.

Im concerned that the rental company will look to cover this under their insurance. Their t&cs say nothing about 3rd party damage.

However I do remember then a similar thing happened in my own vehicle my insurance company told me the excess didnt apply to 3rd partly claims.

Anyone have any similar experience?

thanks in advance