Not being able to cover the mortgage is a total non factor, either you have a halachik right to raise the rent or you don’t. As a worker for a real estate company that rents out (among other things) residential homes I can fully understand the frustration of not being able to raise rent, but G-d has a plan and it is called Halacha, and the only place to get a real answer on what Halacha says is beis din. You can’t lose out by following, no mater how enticing it may seem to go to court(unless you get a heter arkuois).