Why does our kit invoice become a piece count after delivery?

We ordered accessory kits for the UR5e fixture-loading exercises. Each was meant to contain a locating block and its matching fastening parts. I checked the seller's final contents message before paying because I did not want students mixing loose hardware. The sealed carton contains enough fastening packs but fewer blocks. The seller now says the quantity on the invoice covers individual pieces, not complete kits. That does not match the invoice description or their own message. Has anyone had a shortage resolved using the agreed kit contents when the seller keeps returning to the total number of pieces?