claiming esa as a couple

Catt7

My Partner and i have recently moved in together and are both claiming pip and esa, my partner was on the high rate contribution based i believe, and i am on the low rate income based,  my partner recieved a letter saying he wasn't to be paid anymore esa and upon phoning dwp we discovered that we are on a joint claim, but are only recieving 300 odd per fortnight, a drop of nearly 900 pounds a month, Is this right? Would it have made any difference if he made the claim for us? Is they're anything we can do, should we appeal etc, thanks