The missing part, and how not to promise it twice
Write down the part, the date you gave, and the bay, so the shop does not promise a day the shelf cannot meet.
Write the promise
«I'll call when it arrives», with no part and no date, is a promise that gets forgotten. The order should say what is missing, on which car, and what the customer was told.
The date you give is the supplier's date plus the time the shop needs to fit the part. Promising the day the truck «should» leave is promising the best case. The customer remembers the day.
Do not book an empty bay
A booking to fit a part that is not here takes a gap and annoys two people: the customer who comes, and the one who could not. Until the part is on the shelf, the car waits. It is not booked.
When the part arrives, record the stock movement and then offer a time. Part first, bay second. That order avoids the call to postpone.
One version
If the counter says Thursday and the bay says next week, the customer believes the date they prefer and argues the other. The live date is the one on the order. The chat only repeats it.
If the date changes, update the sheet and tell the customer once. You do not need a message every day. You need the change where the next shift will see it.
When it is late
If the supplier misses, say so before the customer calls. A delay told early is easier than another «almost». Offer the next real gap, not a symbolic one.
When you close, check whether the part was used or went back to stock. A part received and not fitted, and not put back on the count, gets ordered twice. Goods in and goods out both have to exist.