New Employee Pay Question

I accepted a school nurse job at another school district this year. I received a letter from the school"Chief Financial Officer" yesterday. He states the annual PEIMS report revealed an error in my pay. School started August 13 and I was hired August 20. This is in Dallas. He said my pay was supposed to be prorated and it wasn't for Sept, Oct and Nov. So starting December, my pay would be reduced by $96 a month. I responded that it wasn't my error and that the district should swallow it or even split the difference. He said it was illegal to give public fund as a gift to me. And that there was no other options. I said I had talked to labor law experts and they thought it wasn't fair. I told him I accepted the job and turned down other offers according to the salary I was given and signed a contract. I have a meeting with him in the morning. The 5 days I didn't work, mounts to a total of $900. What do you think about this matter? Would you take the cut quietly or not?