This is common and usually the amount added to your balance consists of back payments that were not made or missed in addition to a relatively smaller amount in fees to complete the modification. Did you confirm with Citibank what the $26k included?
Modifications unfortunately on average hurt more than helped borrowers. If you signed the promissory note four years ago and paid off or sold you may not have recourse in Florida anymore. If there is unpaid balance and you still own the property you could go back to Citi directly and fight with them. I am not sure why you believe this is "mortgage gouging" or that any such law exists. Usually a mod gave you 40 years with intial cheaper payments for three or five years but still everything is paid off. If you are now out of the introductory cheaper period and struggling there is no program or incentive for Citi to do a new modification. Do you have equity to sell now?