Amazon canceled a refund a seller gave me

I purchased a product through Amazon for approximately $400 that was missing multiple parts needed for assembly. Following guidance from an Amazon customer service representative, I contacted the seller through Amazon's messaging system to resolve the issue.

The seller promptly shipped replacement parts.

After the product was assembled, I discovered another significant issue with it that made one of its features unusable. I provided the seller with a video demonstrating the problem.

The seller responded by offering to send me yet again, a replacement part. But I declined this offer because replacing the part would have required disassembling the product that I had already spent considerable time assembling.

The seller replied that they understood and voluntarily offered a full refund for the product due to the numerous issues I had experienced, which I didn't request. However I thanked them and told them I appreciate the gesture.

I then received an email from Amazon stating that they cancelled the refund because I reported that I didn't receive the item but the carrier confirmed delivery of the shipment. I never reported the item not delivered. Only that the package was missing parts. The email also noted the last few returns that they've processed for me and said that they're warning me I may be in violation of their terms.

These were all approved returns. I don't get the issue. Is Amazon not wanting people to take advantage of free returns that sellers offer? That's one of the only reasons why I would even shop at Amazon to begin with. I referenced Amazon's terms about refunds and didn't see anything about a limit on requesting refunds. And why are they claiming I reported a an item not delivered when they could easily see that never happened and by referencing my call history with customer service and the messaging history between me and the seller?