1. I agree with Tango. It is SOP to deny your claim, unless they have been caught "bang to rights".
2. This is clearly an Operational issue under their control. The ATC stuff is a smoke screen. if they knew the plane was going to be c 4 hours late then they had plenty of time to fix another plane.
EZY denied my claim for some time. It was an Operational issue.
Keep at it! The Small Claims Court is a good suggestion.