iDNS is a scamming company that has been active for several years under different disguises. They very cleverly structure/ design their letter to resemble a bill with tones of urgency in it. This has been reported to iCANN and they should be banned. Sadly, they will only pop up in another country's extension, like .ag, .ae instead of a legit .com. Do not fall for this, legit companies will only communicate with you directly through your email address. Nobody sends snail mail - especially domain related stuff.