I'd be frank but polite with them.

Tell them flat out that you will not be paying for work or parts you didn't authorize. Tell them they are welcome to replace your old parts and keep the new stuff you didn't want (for free) if they wish.

Make it known that they have now done this twice and it's unacceptable; if it continues to occur you will find someone else to do the work. (They are, I assume, friends; let them know what the issue is in no uncertain terms and give them a chance to fix it first IMO).

Let them know that you are OK with repairs taking longer IF they vet the repairs/options through you first, but that they MUST vet the repairs/replacements with you first either at time of drop off or as a problem is noticed. (ie: I'm fine with my repair taking longer because we had to play phone tag)

Many shops, I'm sure, get used to the type of customer that don't know and don't care what goes on the bike, but they want it done ASAP. Making it known that you aren't that person *should* solve the issues and if not then it's time to find a mechanic that will listen to you.