RFID IC (MFRC522) with 50-Ohm antenna (taoglas fxr.01.A)
After a long night I figured out what to do.

This PDF, Design of MF RC500 Matching Circuits and Antennas (alternative source), has a detailed info about how to implement what I wanted.

This is the image of the circuit I implemented, just needed to change some values of caps, but all near to the ones in the image. Worked perfectly.