I cbf to record myself humming it or something but it's a 2 note melody (with note B being the higher pitched) that goes
A B AAB AABA AB
Edit: I don't know if all the wildly different and incorrect replies are a bit, or if this post really is just that vague, but here it is hummed https://voca.ro/17WHcwM48PVa
I don't mean for this to come off as vibey, but in the humming example you definitely sang 6 different pitches, not the two notes you posted originally; this might be why you can't find the song anywhere. The thing is, I think you sang it correctly, because you sang it (almost) the same both times you did, and our ears and aural memory tend to be more accurate than our transcription. That being said, the melody I transcribed from your humming was - G C F#F#B EEAE EG. On the repeat you sing it slightly differently with an E C at the beginning instead of a G C. The rest of the second time I believe you sing the same pitches, their tonality just shifts a little flat (which is totally normal to do when singing from memory). Anyway, I hope this helps a little on your journey to find the song!
What's a note
Edit: also for what it's worth, the tapped version sounds more correct to me than what I hummed
A note is a musical pitch. Upon re-reading the post I now understand why I was so confused. You were talking abstractly about the notes using A and B as placeholders, not actually referring to the notes "A" and "B" (it seems like others in the thread had this same fundamental misunderstanding). The tapping is pretty much rhythmically the same as what you sung. That being said, you're looking for a needle in a haystack here comrade. The notes I posted are what you sung tho, if that helps anyone else out who may recognize them.
I was making a joke about my lack of musical knowledge, but yeah A and B were just placeholders. I wouldn't even know what they sound like