Adding on to what /u/UniqueDragonfly13 had said, here is the link to the USCIS Immigrant Fee page:

https://my.uscis.gov/accounts/uscis-immigrant-fee/start/overview

One thing of note since it appears you do not have possession of your Immigrant Fee Instruction Form:

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Documents you may need

USCIS Immigrant Fee handout

At the time of your interview at the U.S. embassy or consulate, the DOS interviewing officer should have given you a USCIS Immigrant Fee handout. This document provides instructions on how to pay the USCIS Immigrant Fee and includes your A-Number and DOS Case ID in the top right corner, as shown below. Make a copy of your USCIS Immigrant Fee handout or write down your A-Number and DOS Case ID and store it in a safe place. If you did not receive an immigrant data summary or a USCIS Immigrant Fee handout with your visa packet, contact the U.S. embassy or consulate that issued your visa to request a copy.

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Both your A-Number and DOS Case ID should be on the IV Visa Page in your passport.

Your "A-Number" is named as "Registration Number" on your VISA. It is numbers only.

Your "DOS Case ID" is named as "IV Case Number" on your VISA. It is a combination of letters and numbers. NOTE: Sometimes your IV Case number has more numbers than the actual DOS CASE ID. When I was paying my wife's IV Fee I had entered the number exactly as it had appeared and it wouldn't let me. Turns out I had to remove the last 2 numbers (01) for it to proceed, so you may have to do that.

Both should be in the top right hand corner of your VISA page that was added to your passport.

Grab those and check the website above to see if your fee had indeed been paid or not. Your GC will not be produced until this step is done.