Bought Pro Unlocker from Amazon - can no longer download it
 

I purchased the Acar Pro Unlocker via Amazon in December of 2013. I had been using Acar on my Nexus 9 tablet, but recently sold that tablet, and now have to use Acar on my Moto X Android phone.

Unfortunately, Acar won't let me import my backup file containing years worth of data without having Acar Pro, and I can't re-download the Acar Pro Unlocker, because Amazon no longer sells it, and no longer lets me download it. And I'm not going to pay another $6 for it.

How do I get Acar Pro functionality back?

I've sent several emails to support about this in the last few weeks, but have received no reply.

Technically we no longer support the unlocker from Amazon. So you would need to buy a new one from the Google Play Store. As a courtesy, in some rare cases, we have refunded users who bought a second unlocker via Google Play Store. In order to request a refund you would need to contact support at fuelly.com. The only issue right now is we have a HUGE backlog of users with issues from our iOS app upgrade a couple weeks ago so getting back to your support email might take some time.

To add on to Andy's note above-
aCar Free allows you to 'pick up where you left off' in a sense that if you freshly install the Free version, it immediately gives you the opportunity to restore from backup. Ensure the backup is in the /zonewalker-acar directory prior to running aCar Free for the first time. Then launch it.
If you've already installed the Free version (which it sounds like you have) then simply delete and reinstall (remember to move your backup to the /zonewalker-acar folder).
Keep in mind, any data you've entered in the free version will get wiped upon deletion. So make note of them so you can re-add.
Alternatively, you can go into your App Settings via your device's app manager and clear data there. Same as deleting/reinstalling. Gives you a blank slate and the app will consider your next launch the first launch and ask you about restoring the backup.