If I have -1 of something then I have nothing

Negative numbers mean you owe something. For example, I'd you have $6 but owe your parents $10, you have -$4 unless you pay it off or gain more debt.

But that's still not having any...

But it doesn't mean you have 0. You have less

Physically, it means you owe something, yet you don't have any (aka 0) bc you can't own -X things :/

Yes but to owe something is to have less than 0. Also, if I asked what your acceleration rate is and you are slowing, you have a negative acceleration because 0 would mean you are neither speeding up or slowing down.

Motion-wise is correct

Even in this sense it proves negative numbers exist and are not 0. Now to really stress out we could discuss imaginary numbers

Technically, yes :1

No, you're in debt.
You have physically nothing, but if I give you 3 apple when you owe me 1 (aka you have -1), you end you with 2 apple.

If you really want someone that doesn't exist, use "i", the imaginary number.