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:

https://www.irs.gov/pub/irs-pdf/p4164.pdf#%5B%7B%22num%22%3A589%2C%22gen%22%3A0%7D%2C%7B%22name%22%3...