Do you have the IRS Form 575 that lists the name and number? On page 2 is the control as a four letter
.
If you can't get the letter use this as a resource to call https://www.irs.gov/businesses/small-businesses-self-employed/lost-or-misplaced-your-ein
Just as George says.
Publication 4164 is also a good reference for MeF. This section about name control may be of interest to you too:
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