possible failure Logic board iphone 7+

Have exhausted all remedies so asking for any further thoughts. After upgrading iphone 7+ to IOS 13.6, phone unable to make or receive calls, Siri would not work, microphone failed, voicememo not functional but could play videos and audios, and wifi functional. Ultimately, after apple tested, by process of elimination, advised likely board failure. Tried downgrading, reinstalling, etc, but no change. Any possible solutions including sending phone to third party for possible repair estimate, and who is reliable?