Arthur,
If I understand you right, the well under your section was drilled prior to the 2nd well. First, I would call OCC 405-521-4457 (Junior) or 405-521-2613 (Dana) and ask when the first well (Lavera 5) went online. This is when the first oil was sold; you should have gotten a check 6 months after that date.
Also, ask if they have any records as to how much oil was sold under that well. Get the API number, name of buyer, etc. Then you may have to go to the Tax office and see what was sold under that well. You will want to do this even if Devon did make a mistake as they may have taken taxes out of your check, so be sure you get it back.
Now you may need an attorney to help you. I have several names of good attorneys in Oklahoma City. One I really like as he does a really good job, fast, complete, and reasonable for an attorney.
If you make me your friend on this forum, I can forward his name and also other good attorneys’ names.
Virginia