There are three things you can do. The first one is to search for the computer-generated notice which was sent to you by IRS because it contains your number. If it is not available then you can report your case to your bank or state agency, if you have used it there before, and they will secure a copy of the EIN in your behalf. The last option is to request a copy of your EIN at IRS. You can talk to a customer assistant via IRS hotline at 800-829-4933.