Keyword overlap is the right call for a knowledge base this small, but the prompt is not the guard. If the best chunk scores zero, skip the model and return the fallback yourself, because a model told to use only the excerpts will still answer from memory when the context is empty. "Where is my parcel" also shares almost no tokens with a Shipping times heading, so a tiny synonym list (parcel, shipping, delivery, refund, return) stops those from falling through. Put the human support hours and a line asking for the order number in that same fallback. Most of these questions show up when the inbox is closed, and a refusal with no next step just sends people away. Before each deploy, run two or three questions you know are not in the docs so an edit cannot quietly turn the bot back into a guesser.

Neil