Who says it was mailed? The IRS or Turbo Tax? Did you efile? Was it Accepted? Maybe you didn't finish filing it or it Rejected. When you log into your account you should also see the status and if it was Accepted or Rejected, Started, Printed, Ready to Mail, etc. what does it say?
Then when you efile you get back 2 emails. The first email only confirms the transmission. The second email says if the IRS (or state) Accepte.d or Rejected your efile. Check back though your emails if you have them.
If Turbo Tax says Ready to Mail that means you had to print it out and mail it to the IRS yourself.