It sounds like you are stating the original W2 showed the correct dollar amounts that were actually paid to you and actually withheld for SSA taxes (even though some SSA taxes were inappropriately withheld). Then the corrected W2 shows an incorrect SSA withholding amount.
IF that is the case, you may want to contact your employer again, and request another revised W2, going back to the original W2's accurate data. Then use that data on your return. (The W2 should show what actually occurred, regardless of whether it was a mistake.)
If that does not work, I refer you to https://taxmap.irs.gov/taxmap/faqs/faq_01-015.htm
Pay particular attention to the section "I received an incorrect Form W-2. My former employer won’t issue me a corrected Form W-2. What should I
do?" Refer to topic 159 and form 4852.
Topic 159 describes how to get a transcript from the IRS with info actually paid. It is accessible here: https://taxmap.irs.gov/taxmap/taxtp/Tt150_18-010.htm This data should match the Year-to-date data on you final 2018 pay check stub.
Form 4852 and instructions are located here. https://www.irs.gov/pub/irs-pdf/f4852.pdf
