You would have a code D in box 12 on your W-2 form where your 401-K contribution would have been listed. It is possible you were enrolled without realizing it, as sometimes enrollment is automatic. If you didn't receive a distribution from the pension plan, you will need to contact your employer and inform them of that so they can correct the 1099-R form they sent you. You don't need to report the distribution on your tax return if you did not receive it, but if you can't get your employer to correct the 1099-R form the IRS will likely assess you tax on it sometime down the road. If that happens you can explain what happened but they will probably tell you to contact your employer and get it corrected or they will deny your claim.