If you purchased Guitar Hero Live within the last year, you are entitled to a refund.
Activision is offering full refunds to US customers who purchased Guitar Hero Live between December 2017 and January 2019.
To receive a refund you will need to submit a Claim Form through the website by May 1. A receipt or a credit card statement can be provided as proof of purchase. Once Activision verifies the claim, it will issue a refund.
If you no longer posses the proper documents, the company will still attempt to verify the purchase.
Receipts or credit card statements can be used to verify purchases, though Activision will attempt to verify the purchase if neither is available.
As GI.biz notes, the publisher has not offered an explanation for the refunds, but it's likely due to Guitar Hero TV servers being taken offline back in December.