Hi thanks for your reply.
First I changed the RFID's SDA and RESET not the I2C if I am not mistaken. I changed the pins for SDA from 53 to 8. As I have read in this article https://www.arduino.cc/en/Main/ArduinoEthernetShieldV1, pin 53 must be left unused or the SPI would not work. Additionally I have used pins 50-52 for the RFID MFRC522 and now I think it must also be left open?? Please help me.
Second would you please enlighten me which library should I use. Currently my library supports SPI.