The iPhone 7 was released in September 16, 2016, making this phone just over two years old. However many iPhone 7s have been made mostly obsolete at no fault of the owners due to a major malfunction that has taken away all ability to use the microphone (for calls, facetime, etc.)
Apple's only current solution is to offer a refurbished iPhone 7 replacement to customers for over $300 with no guarantee that the replacement won't come down with the same issue. Prior to that Apple offered free repairs for just 2-3 months between May to July 2018. It's still not completely clear whether this is a software or hardware issue though some people claim that updating (to iOS later than 11.3) caused the issue. It still remains a problem after the newest iOS 12.1.1 update.
Apple's document then provided troubleshooting steps for its service providers to follow, including disconnecting any Bluetooth headsets or accessories connected to the iPhone. If the issue persisted, and the iPhone was out-of-warranty, Apple advised service providers to "request a warranty exception" with the company. For a short time, Apple Stores and Apple Authorized Service Providers were able to proceed with repairs at no cost to the customer.
The exemptions abruptly ended in July of 2018, though, when Apple deleted its internal document related to the microphone issue and prevented free repairs from being processed through its service portal. Since then, many Apple retail and support employees have refused to acknowledge the policy ever existed.
The original article about the issue and Apple's acknowledgement of the issue in May 2018: