Yep keep schtum,you had it serviced through a guy you used to work with,the old parts were shown to you and the van drove perfectly afterwards,the book was stamped by whoever did the service,your not sure who that was as of course the guy that recommended him your no longer in contact with.
You know the van was serviced correctly and the reason you did this was because you've been caught out before with the work not actually being done and being charged for it hence you insisted the old parts were shown.
End of story.
Garage can't chase you for fuck all,ludicrous.