You should naturally ignore the letter. In fact, if you receive an envelope with the Domain Renewal Group logo on it, the best thing to do is not open it, obscure your address, write 'Junk Mail; return to sender' on it, and put it in your next convenient postbox. Or just bin it, whichever suits.
The letter I received was offering a one-year .net renewal for £20, which is extortionate.