Product: Student loan

I have been on an IBR ( income-based repayment ) plan with Nelnet for the past few years. Since XX/XX/XXXX, my monthly payment has been {$580.00} month. In XXXX, after submitting my annual required application, despite no increase in income in XXXX from XXXX ( just a change in payment frequency from every 2 weeks to bimonthly ), I was informed that my payment would be increasing to {$620.00}. When I called to inquire about the justification behind the sharp increase, I was told by the customer service representative that my payments should be actually in the {$400.00} range after I provided him with my income from my pay stubs. He advised that I send him my pay stubs by fax in lieu of my tax returns that I previously submitted through the automatic data import process to have it correctly calculated. I did this and when I saw no update to my bill, I called again to check the status. I was told by that representative that I shouldve also submitted a new application, but after giving her my salary info, that she was calculating a higher payment than the original {$620.00}. As this wasnt my intention, I asked her to leave it alone. 

So it was to my complete surprise that the next bill I received ( in  XXXX ) increases to the amount of {$650.00}. I called back to inquire and complain and was told by another representative that my bill should actually be over {$700.00}. Due to her rude attitude and insistence on cutting me off rather than listen to my explanation, wrongly insisting that I made more money than the year before ( although I clearly did not ), I asked to speak to a manager to get the issue resolved. This manager said he found the problem in the previous calculation and according to his calculation, my bill should be reduced to about {$580.00} and said he would resubmit to underwriting. So again, it was to my complete surprise when my payment instead increased to {$640.00}!

When I spoke to this manager again, he apologized and said that the {$640.00} must be the correct payment amount. So despite my not having an income change, my bill increased by {$65.00} within one year.

Throughout this process, I spoke to 7 different people who all gave me wildly different calculations based on the same salary. I dont understand how this is possible. If Nelnet dont have a proper formula or their customer reps arent trained to make calculations ( one of which is evident ), they should not!!! It is unfair to me as I feel that the first representative who incorrectly told me my payments should be in the {$400.00} range misled me and resulted in a greater increase than what I was already being charged. Calling them only hurt my situation further, and honestly I am scared to ever call them again because I feel taken advantage of by them and at risk for undue and incorrect increases just by doing so. I question if this practice is intentional to try to force increases from payers. 

Note : My other federal student loans serviced by XXXX, only increased by {$10.00} in XXXX with the IBR. This makes more sense and better aligns with my payment schedule change, so I simply dont understand how Nelnet can justify their sharp increase.