EasyJet complaint: Lost luggage

My daughter Abigail Davies has failed to receive her suitcase since we arrived at LGW from Rhodes on 8th July on flight EZY 8788. Two cases among our luggage were lost. Bar codes are: 0000 XH593354 and 0000 XH 593341 Two cases have since been delivered to my home. One belonged to my younger daughter Faith Davies, the other belongs to an unknown person whose surname is Davis who was on an Easyjet flight from Athens the same day as our flight from Rhodes. When my daughter Abigail contacted your lost luggage team she was told it was her responsibility to take the luggage of the unknown person to Gatwick Airport. I challenge this viewpoint. Easyjet charge a considerable sum of money £40 per case per flight to take hold luggage on board. We are entitled to expect it is securely returned to the right person at the end of the trip. We should not need to incur additional petrol costs delivering luggage which you cannot process properly.