My payment schedule for my private student loans increased 900 dollars over the course of a month

Hi everyone. Last month i got a letter showing my repayment schedule for my private loans showing they will be 1263. Which is already tough but doable, i will save, have a second job, i took them out myself i know.

But this month, i got a new repayment letter showing they increased to 2100 and some change a month. i called my lender (Ascent) and they were no help. They said that this was included in the loans payment schedule and basically wouldnt go into more detail.

Is this even legal? I mean i got the document saying the 1263, which has been on the website and on all documents for years. And now all of a sudden it jumped up almost 900 dollars? I have no idea what to do. I can't afford over 2k a month.