Problems with some roofing..

chappers

I think your best option is to keep hassling him, you have 6 years to make a claim against him basically if you want to go down that route, but as you have already paid him you would really have to get the work done first and then go after him for the money.
Do you really want him to send the same guy who did it in the first place.
As Furts says there is aright way to do this and your ridge should last for years easily 50 years plus.
First the mortar should be strong enough and of the right mix about 3:1 is about right and I would use 1 part sharp sand to 2 parts building sand, also as has been said the mortar shouldn't be blobbed on in one big dollop as it will shrink away from the ridge tile slips or pieces of broken tile should be used to build up the layers of mortar under the tile this will stop the mortar shrinking and cracking under the tile.
The right tile for the roof pitch should be used so as not to have too high a pile of mortar underneath nor for the base of the tile to sit too high off of the roof, it shouldn't be necessary to point under the bottom of the ridge tile on a slate or plain tiled roof, although a very thin bed of mortar can be applied.
It also shouldn't be necessary to bed the whole length of the ridge tile on a solid bed of mortar, but just at the joints and about 4" either side, but I always bed a thin strip on either side of the roof about half way down each side of the tile.
Also it is a good idea to soak the tiles in water before bedding as this will help the mortar actually bond to the tiles.
As Furts says most roofers let alone builders don't bother with this level of detail, but it's the way I was shown and the way I have always done it since.
As you have witnessed if not done properly it will fail very quickly and the consequences of a fallen ridge tile doesn't bear thinking about.