The Courier Guy -Cannot rectify their mistake and terrible for Business

The business uses The Courier Guy to send parcels to the clients throughout the country. We prep everything with the correct waybill number attached to the parcel. The Courier who collected swapped two parcels. This was in November. The one client still does not have the parcel. The is after multiple emails and phone calls. Could you please make sure our client gets the parcel and the refund she requested? This is a terrible reflection on the business and can do damage to a business for which The Courier Guy is liable. The contact person was Tonia Human. There is a thread of 16 emails and still, the client is without the parcel nor the refund!