Paragraph correction, please.

Hi,

I posted this question yesterday, but I guess it wasn't cleare enough. Here is it again; would you please correct this paragraph. I'm describing this case to a friend of mine Thanks alot.

"I work as a teacher and I get paid for each class in advace. So, when a student wants to take (a?) class, he/she calls me and we set up a time for class, after he pays for it, say, a two days before. The problem is that when the student tells me that he can't attent just few minutes before class, I have to consider them as present and not give them there money back, so when they want to take another class, they have to pay for it again."

So, when a student tells me that he can't attend class he chose its time, I would say to him; I am sorry, but because you didn't apologize for not being able to attend class, you would be considered as present and lose the money you paid. You have to apologize at least 2 hours before class.

Thank you veery much.