Matthew 17:24. 'Does your teacher not PAY the Temple tax?'No. Τετέλεσται cannot be applied to debts. You have the wrong word.
The word you are speaking of is very close, at least to our eyes, so I understand your mistake.
The word you define is τετελώνηται ("paid in full"). This is the word found on ancient notes.
Τετέλεσται refers to something being completed, acomplished, or finished. But never a debt (something like building a house, completing a college course, finishing a project).
While these may be related words they are different words.
The fact Τετέλεσται cannot mean "paid in full" itself does not disprove your theory. It just does not prove it either.
That is why the proper title for PSA is The Penal Substitution Theory of Atonement. Like The Substitution Theory of Atonement, it cannot be proven using Scripture as the standard.
And same with Christus Victor/ Ransom Theory. With these the facts can be proven BUT what makes them theories is the idea that specific aspects are the main focus (Scripture does not prioritize focusing on Christ's victory over evil against Christ's obedience to God, for example).
Romans 13:6. 'For because of this you also PAY taxes.' The Greek word in both cases is teleo from which we get tetelestai.
The fact that both of these verses mention taxes cannot be taken as proof that it never means anything else but paying taxes. The root meaning of teleo is to finish. When you pay a debt it is finished. The Lord Jesus taught us to pray, 'Forgive us our debts.' God has answered our prayers by sending the Lord Jesus to pay the debt of sin that we owed. We owe it no more; it is finished, paid in full. Penal substitution.