SAS Dance Charging Customers Extra Money Gilbert, Arizona

My daughters had been dancing in this school for a few years.  I paid hundreds of dollars for costumes, pictures, dvd's, recital fees, monthly classes etc. I pay this school for the months of January to May with the girls doing their recitals the first week of June.  For some odd reason this Aug. they decided to bill their customers for 1/2 of the month of June with no warning.  I emailed them of this issue, their response back was "We billed all of our customers that withdrew their kids for half of June."  I then replied, " Well I never withdrew, I am a regular."  They would not write back with a response.  I wrote them once again explaining how much money I poured into their school and how I will not pay this bogus bill for services not rendered.  I then told them I would never come back to their school and word of mouth is a powerful thing.  I figured they were short on money and decided to come up with a plan to charge people to get that extra money.  That is what I call bad business and highly unprofessional!  I do have the emails to back up my statement.