Something fishy with invoice

Expecting a parcel. Received missed calls from fedex customs dpmnt. Thought there was an issue with parcel. Called them back and while doing that, i checked system and my parcel had been released by customs. Call centre agent stumbled on words and saying oh its been released not sure why they called you. They think they phoned you to ask for email address for invoice (before it had even been submitted to customs). Then while still unsure of what they doing they say i have to pay an amount to them of R600 when my tiny parcel was already released from customs????? It would have obviously say it was held by customs if i had to pay an amount????? ***** on my behalf. Dissapointed!!!