Damn the £30 refund this is way more serious this is in "lie down on the floor whilst I kick your ass for the next 20 minutes" league or find me another frame this size in this condition numbnuts
This is exactly why I do all my own work on my bikes.
My sympathies bud. May I suggest you make a fuss when they are at their busiest (sat afternoon?), as you are more likely to get a 'stop making a fuss in front of the other customers' type settlement. If not, stand there, with frame in hand, showing everyone what they did.