Hmmm, I don't really understand all the weird stuff that's going on with your Tamagotchi, but this might be the sign of a glitch. Happy reseting, pal. (not happy)
Glitches happen when your tama is screwed or you press something strange. Have you ever dropped, punched or tried to twist your tama? Or pressed some buttons during something?
Try resetting your tama. It shouldn't evolve again after it's an adult, unless you refuse them matchmaker. Then it will evolve into an oldtimer.
p.s. This is strange... my Kuchitamatchi evolved into a Hinatchi... at 0! There was no sound or anything to say that it was about to evolve. It just suddenly changed character, just like that.