no real explanation to be honest. At the moment I am suspicious as to whether they fitted the right oil filter.... Either way end result is the same. Cracked block meaning new engine needed
Ah jeez it gets worse. Was the oil filter changed several weeks before the problems started? Rolling right back to then....Where there any indications of any problems prior (hard starting, smoke, coolant temperature?
I'm not sure that using the wrong oil filter could result in a cracked cylinder head, bore or block. Maybe... but obviously excessive oil pressure can create all kinds of problems. Normally an engine would have pressure relief to release excessive pressure back to the sump, again I don't know these engines well enough to talk about specifics.
It's a hard case to fight, but unfortunately if the garage has incorrectly installed something, or incorrect diagnosis then they need to own it. For example the alternator and other parts fitted....if the real problem was a cracked bore, block or head. Diagnosising problems is not easy I do admit.
Back to the actual problem. I would want to see the crack, maybe see if it can be repaired. "Then of course need to figure out what caused the failure in the first place."