quote from african pilot
NAC discovers yet another aviation scam
NAC applied for clearance through West Africa when suddenly a letter arrived to say we could not get clearances as we were "so called" in arrears with ASECNA. We most certainly were not in arrears so upon a query it was noticed that this letter was not even on an ASECNA letterhead nor was the bank account one belonging to ASECNA. The letter also indicates that we should pay in advance. From this letter one can clearly see that this is a scam and probably originated from some government organization dealing with clearances and not from ASECNA.
reminder as merlin points out also check the originating address
asecna is a .org not a .com