Healthcare premium deduction

No, that's not correct. You might have misunderstood what the specialist said. The amount shown with code DD is the total cost of your health insurance. As you are aware, most of that cost was paid by your employer. Furthermore, the amount that you paid yourself was almost certainly deducted from your pay "pre-tax," which means it was not included in your taxable income. Since it was already deducted from the taxable income shown on your W-2, you can't deduct it again on your tax return. So you probably cannot deduct any of the health insurance premiums.

Box 12 amounts with the code DD signify the total cost of what you and your employer paid for your employer-sponsored health coverage plan. Code DD amounts are for informational purposes only—they don't affect the numbers in your tax return.  The amount reported with Code DD is not taxable, but neither can it be claimed as a tax deduction (medical expense) by an individual taxpayer.  Therefor, You can't deduct the portion of your premiums that your employer pays, for example, or any premiums that come out of your paycheck pretax.

The link below will provide additional information:

https://www.irs.gov/affordable-care-act/form-w-2-reporting-of-employer-sponsored-health-coverage