If it’s like the pack on my old Corsa they are not the best quality of items and water gets in and sets up corrosion that leads to failure. You can’t see this damage when the coil pack is in position. Perhaps the garage took them out to do the plugs and the corroded pack broke.

If so I don’t think the garage is to blame. You can of course ask if they will be charging for a new pack and hope they make a contribution and you may be lucky. But look at it another way, if they were due to fail then it’s best to have replaced them anyway.

On the Corsa it was a few minutes work so labour cost should be low.

Our 1998 Focus 1.8 petrol started to misfire very slightly at higher revs when it reached about 70,000 miles. The wisdom of the forum suggested a new coil pack and at £30 for a genuine Ford item it was worth a try. When I started removing the leads form the coil pack part of one of the plastic bits that the leads fit onto simply fell of and looking at it the crack was not new. Noted it but could not believe that it made a difference. Fitted new coil pack and all was well fro another 50,000 miles.

Posted my findings on the forum and it was a new one on them but one posted suggested that a crack in an old style distributor could cause a misfire so why not a new style coil pack. Seemed logical enough but at least they are cheaper than a distributor. Still have the old coil pack in the garage, stuck the piece back on with araldite and kept it as a spare, never tried it to see if it still misfired though.