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When you say they've charged you too much interest, do you mean that each month an incorrect amount is accruing, or that they have applied too much of your payments to oustanding interest. I would ask for (or find on the website) a detailed loan statement that outlines how much interest is accruing each month as well as any previously accrued but still outstanding interest and fees. It will be easier to figure out what is going on with an exact breakdown to reference with the rep. It is possible that they did not capitalize some or all of that interest coming out of rehab, and it really is to your benefit that they not capitalize it, otherwise you would be paying interest on your accrued interest.