On the phone

An aged person is teaching a boy how to use correctly the telephone.
After having dialed wrongly a number and getting an answer, the "pupil" hangs abruptly the phone.
Teacher: It musn't be made.
Pupil: Why must I talk to the other person if I have mistaken the number?
Teacher: [b]То в твой воле [/b]("that depends on you", is what I would like to hear; what I really hear is: то в тем воле/я. Here obviously the genders don't agree). If you were not mistaken, you wouldn't bother uselessly the other person. You must apologize necessarily.
So the meaning of misunderstood words must be something like "You must do it" ; "it is in your obligation" and not my translation. Please, which are the words that fit to meaning and furthermore to the grammar

"То в твоей воле" sounds rather old-fashioned. Could it be "Тем более"? (~ Even more so)
It's a little abrupt too, but still it's a more natural turn of phrase.
Audio would help.

It is in 2:52
Урок 2 Разговор по телефону Давайте послушаем
http://www.gwu.edu/~slavic/golosa/audio/audio2-4e.htm
Thank you.

Yes, she says "Так тем более". "Так" is used for emphasis here and does not mean anything in particular.

Thank you.