You would have to contact TurboTax product support to request a refund. Use the word billing when setting up a call back:

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

The TurboTax 2018 desktop edition is only available in Deluxe, Premier or Home & Business.  You could not have purchased the 2018 Basic desktop edition in 2020 - https://turbotax.intuit.com/personal-taxes/past-years-products/

The TurboTax online editions are only for tax year 2019 - https://turbotax.intuit.com/personal-taxes/online/

What exactly have you purchased?  What tax year are you trying to complete?

If I read their post correctly, they purchased Basic 2018 in late 2018 or in 2019 and prepared their 2019 tax return with it. They then mistakenly thought they could just upgrade their 2018 product to get a 2019 download. I could be mistaken and if so they can clarify it. 

CORRECTION: If I read their post correctly, they purchased Basic 2018 in late 2018 or in 2019 and prepared their 2018 tax return with it.

@Texas Roger   You meant they did their 2018 return with it, right? 

@VolvoGirl  Yes I meant their 2018 tax return.