I wanted to amend my taxes. I filled out the paperwork and put it in an envelope to mail. However, I can't remember if I mailed it. Who can I contact about this?

So you did not use a mailing service that would track it--like UPS or certified mail?

A 1040X cannot be e-filed.  It must be printed and mailed.  It will take about 3-4 months for the IRS to process an amended return.  It is a good idea to use a mailing service that will track it, like UPS or certified mail, so you will know it was received.

Wait about 3 weeks from mailing and you can check the status of your amended return:

https://www.irs.gov/Filing/Individuals/Amended-Returns-(Form-1040-X)/Wheres-My-Amended-Return-1

If the amended tax return, Form 1040X, was received by the IRS then the status of the tax return should be shown on the IRS website for amended tax returns - https://www.irs.gov/filing/wheres-my-amended-return

If it has been over three weeks since the time you think you mailed the amended return and it is not shown on the IRS website with a status, then go ahead and print, sign, date and mail the return again.  This time use a tracking service from the US post office where you get a receipt when the IRS receives the tax return.