I have had the same problem! ::)
I have made 2 sowings, and have one lettuce from the first, and two from the second sowing. The only reason I haven't complained is that I had similar problems with the 'lipstick' peppers I also purchased from them, which they replaced with a different variety without complaint and apologised; I feel bad going back and complaining again!!
Perhaps we should both email and have a word.........I'm glad it's not just me! ;D