Poor workmanship

On the 12/10/15 I had a new windscreen fitted at like-nu motorglass. On Friday the 30/10/15, I noticed the windscreen was cracked. I called the shop and explained what had happened and was advised that there is a guarantee for poor workmanshop but not if the windscreen was hit by a stone, which I understand as I wouldn't have called them if this was the case. I asked 3 guys to have a look and tell me what they think. All 3 of them said that there was no stone chip and the one explained to me that the crack started from under the beading, that means that the windscreen was not installed properly. My car was taken on the 2/11/15 to the shop so that they can have a look and see that its not fault on our side. A guy by the name of Donovan then said that it is not their fault and refused to replace the windscreen. It was said that it is a generic windscreen and that the rearview mirror was fiddled with etc (what utter nonsense).Now I want to know how can a company like this sell these type of windscreens if they know its not good value? I would recommend no one uses this place with stinking attitudes and such bad customer service and workmanship. I'm taking this further!