I paid for Turbotax for the 2017 tax year and now need to download my return .. why would I have to pay since I already paid in the past?

If you already paid for 2017 Online TurboTax (in PLUS or higher) when you prepared your return last year, then access to the 2017 return should not be locked.  If it is, then here's how to phone TurboTax Support to troubleshoot:

Hours are 5AM-5PM Pacific (8AM-8PM Eastern) Monday-Friday.

FAQ: What is the TurboTax phone number?
https://ttlc.intuit.com/community/using-turbotax/help/what-is-the-turbotax-phone-number/00/25632