Lost lugage

dear,on September 14th 2023, i traveled from Seville to Madrid with the flight IB 3951. I only had a small carry on luggage. At the gate, my luggage was taken from me because it needed to go in the plane. In Madrid, I had a connecting flight to Brussels with flight IB3208. My luggage did not arrive in Brussels and want therefore submit a complaint for financial compensation. The loss of luggage was reported in PIR with number AHL BRUIB21567