If you are an Advantage customer (annual subscription), was your credit/debit card charged around November 7, 2018? If so, we can tell you how to download the 2018 product from your Advantage account.
Or did you only recently sign up for Advantage? If you just recently signed up for Advantage, that would be for next year's 2019 product, and your card will be charged in November 2019.
I really needed the 2018 TT Version. How can I get that?
You didn't answer any of the questions I asked above. So I don't know what you are doing/did. Once it's clear what your situation is, we can tell you what you need to do.
Here's where you should be able to download your 2018 product:
https://shopping.turbotax.intuit.com/app/downloads/
If you don't find it there, or have any trouble downloading it, please report back and describe the situation.