Do you have an iPhone? Then you need to contact the company that delivered your charge card. Ask for the UID number.
If you have an NFC-capable Android smartphone, you can find out the RFID code of your charge card yourself. How? Download the NFC Reader app from the Google Play Store:
Open the app;
Press “Scan a tag”;
Place the charge card you want to read at the back of the phone;
Wait for the phone to read the pass;
You can recognize the RFID code by the label 'ID (dec)'.
Voila! There's your RFID!