I got a letter from a debt collector for a debt from 2014 that i paid in 2017

It’s for formerly unpaid tuition and the letter actually went to my mother’s house so they’re about 3 addresses behind at this point.

I’m certain I paid this off because they were calling me and I was dodging their calls, then the started calling my job and that’s when I paid.

They said if I don’t dispute the debt they will take the debt as confirmed. As of now I don’t think I can find the proof, which would just be old bank statements.

I’ve been advised to not respond since it’s off my credit report and acknowledging it without being able to prove I paid it will give them precedent to put it back on my report.

Is that true? Can I just ignore this?