Hi mate
Dont want to worry you but the exact same happened to mine
They fitted new big end bearings to mine and less than 1000mile later after having it tuned , the new bearings got destroyed taking my oil pressure along with it
Resulting in a fully forged engine rebuild
Took the old crank to a refurb place and they said it had slightly ovaled causing damage to the new bearings due to the oil not being monitored by previous owners and them running it low damaging it
Id double check that the garage who done them for you measured the crank journals
I was absolutely heart broken when i pulled over with an engine rattling like an empty paint can
leon mk1 cupra