Received a mail from a collections agency This is slightly long so please bear with me. This is for a friend and I'll be writing from his perspective.

I am an international graduate student at the University A. In 2016 when I was receiving decisions from grad schools about my applications, I got accepted into University B. I enrolled in a few courses(12 credits) while I was waiting for other decisions. Before I even requested an i20 (a document that international students request when they wish to go to a certain university in the US after being accepted by that uni) from B, I got accepted into A and went there instead for grad school, and consequently never requested an i20 from B.

This week I got a mail from a collections agency stating I owed 22k in fees for the courses I enrolled in all the way back in 2016. I checked every bit of mail, physical or electronic, that I may have received from B in regard to these courses in all my email accounts and residences, which I never did. In fact, the only emails that were found in my gmail were those of my failure to check in after my acceptance from them.

I contacted student accounts at B asking them about this issue and they asked me to get a tuition exception recommendation from the school of engineering. The school of engineering is recommending me for this exemption. The next step in this process is me submitting an appeal to the student accounts department.

This is where the issue arises. Student accounts states within its tuition exception process and guidelines document that appeals for tuition exception must be made within the same term as the courses. I am worried that they won't accept this recommendation from the engineering department despite them knowing the details of my case and never having raised this rule when I spoke to them earlier.

What recourse do I have if they refuse my appeal? I never requested an I20 from B which indicates I never checked in despite their emails to my gmail account they created for me. And most notably, they never sent me any course material or any TA emails for those courses, as is the norm for any courses that people are legitimately enrolled in. I don't have 22k to pay these people.
Here are some educated guesses:  B has a collection agency which they regularly use.  They sell their bad debts to this agency at a (deep) discount and now that agency owns the debt.  They're taking a gamble that they can collect the debt.  (It is very possible that this "separate" collection agency is really just an office on campus.  But that makes little difference.)

I would write the collection agency and tell them that I have never set foot on B's campus and that I don't owe any money to them.  I would make a sentence like, "As an international student, I could not be enrolled at an American university without an i20.  If B cannot produce my i20, that is proof that I never attended there."  I would guess that at this point the agency would realize they lost their bet and go on to the next victim.  

If not, things have entered the "nasty" stage.  I doubt it gets so far, but if necessary, write a letter to B accusing them of fraud.  Your premise is that they know that foreign students are typically naive and apply to many American schools.  If they find that a student applies at B and but attends another American school, then they send a bill hoping the student is afraid of running afoul of obscure American laws.  They use scare tactics to try to collect tuition and fees to which they are not entitled.  Fearful of being deported, many of the foreign students pay the bill.   Something like that will at least get their attention and a human will check the records carefully before they make another move.   The last thing a university wants is an investigation.  At the moment, some bored peon is glancing at your letters or day-dreaming during your phone calls.  You need to get them to sit up and pay attention, and such a letter will do that.  If they look at the record seriously, that should be the end of it.

If not, send the same letter to the local county attorney and/or the district attorney.

Let me repeat that I'm just guessing my way through this given the data at hand.