I filed my 2018 return and it was accepted, yet here I sit a year later I still never received my refund!!! Why?

You asked:  " I filed my 2018 return and it was accepted, yet here I sit a year later I still never received my refund!!! Why?"

Had you checked on it before?  If so, what were you told?

If you are sure the 2018 return was efiled and accepted for processing, then only the IRS can tell you anything about your 2018 Federal refund you didn't receive.  And, unfortunately, the IRS live assistance call centers are currently closed due to the Coronavirus emergency.

If it was prepared in Online TurboTax, you can double-check to be sure it was efiled and accepted.  Log in to your account and at the Tax Home scroll down to the section "Your Tax Returns & Documents".  Expand that section and choose tax year 2018.    What status is showing for the 2018 Federal return (and state, if applicable)--which of these terms:  accepted, rejected, printed, started, ready to mail, or what?

If that confirms that the 2018 return was "accepted",  and if you have NOT yet filed a 2019 return, then it "might" show up in this IRS "Where's My Refund" tool.   The IRS tool says it provides info on the most recent return filed, so that would imply that it might find 2018 if you have not yet filed 2019.

https://www.irs.gov/refunds

In any case, if the 2018 return was accepted, you'll have to phone the IRS for more info on it once they open their call centers back up.