Answered on your prior post for the same subject here - https://ttlc.intuit.com/community/after-you-file/discussion/how-do-i-get-assistance-with-my-tax-return-from-2013-the-irs-is-stating-there-was-a-math-error-and/01/1756460
Normally, the IRS can't assess tax if it is more than 3 years past the date you filed, or 6 years if there was fraud or you understated your tax by more than 25%. You would seem to be past both deadlines.
Who is assessing the tax? The IRS or a state? When exactly did you file your 2013 tax return, and when was the first notice of deficiency? (Not necessarily the first notice you received, if you moved, but when the first notice was sent.). And what exactly is alleged to be incorrect?
Tax Audit Defense will represent you with IRS &/or State IF you are signed up prior to your receipt of a Notice. I was audited once and found it quite helpful and "comforting".