Ok here’s a trick I have used successfully in the past. Remove your frog from the enclosure and Transfer it to to a container with no substrate. Provide a half inch of purified water instead of substrate and something to serve as a hide or haul out (A piece of cork bark works well for this). The water level should be just below the frogs chin. Maintain it in this setup for a while and monitor its progress. Offer food at night. If he is losing weight and still refusing food after a reasonable period in this type of setup a vet visit may be in order. This is essentially a quarantine enclosure. I have “woken up” frogs this way by completely eliminating substrate. It’s also much easier to observe their progress, monitor feedings and provide extra hydration. You can drape a dark cloth over part of the quarantine enclosure to provide some extra security. Again use discretion though. If you feel a trip to the vet is warranted by all means do so.