Left A Great Job For Better Benefits, Now That I've Started The Benefits May Be Taken Away?

I work in home health and visit patients in their homes. When I got hired I was told since I work from home I would be reimbursed for travel from my home to the patient's house and back. Its a great benefit because I live 30 minutes from the main office. When I first started someone from accounting said the policy is to reimburse the distance from the main office to the patient's home (a much shorter distance). I asked my manager (who hired me) about this, and he told me to keep logging my hours from my house and not the main office. He straight up told me to disregard what accounting said and to stick with what we discussed during my interview. Someone from accounting just emailed me about my high mileage (saying it is too high, reiterating their mileage policy, etc), and I'm really concerned because if I have to start logging my miles from the office (and not my home) then its a huge pay loss and I never would have left my former job to begin with. Can my employer say there is this benefit, let me leave my old job and hire me, and then turn around and take it away now that I've been hired? If it makes a difference I was hired in July, so I've been logging my miles from home for 5 months now. I'll be talking with my manager in person on Monday about this.