Your payroll service is incorrect.
The code W is used ONLY for contributions by your employer plus by you through payroll deduction to an HSA, which requires a High Deductible Health Plan (HDHP).
TurboTax thinks it is an HSA because that is the only purpose code W is used for. Have your employer look at the W-2 instructions (note that these are the instructions to the employer on how to complete the form):
"Code W—Employer contributions to a health savings account (HSA). Show any employer contributions (including amounts the employee elected to contribute using a section 125 (cafeteria) plan) to an HSA[emphasis mine]. See Health savings account (HSA)." See page 20 at https://www.irs.gov/pub/irs-pdf/iw2w3.pdf
Yes, HSAs are sometimes funded by a Sec 125 plan, but this AFLAC policy is NOT an HDHP and therefore the premiums should not be listed this way (with the code of W).
My guess is that this would normally appear in box 14 on the W-2.
