Cenlar review: escrow shortage

Every year since we refinanced and Cenlar bought our mortgage from Meridian August of 2012 they send a letter that the Escrow is short. How is that possible, our taxes didn't increase and we are paying a mortgage that balance decreases monthly but the escrow is the same. We have a 10 year mortgage and 3 years down refied for $130, 000 now we are under 100, 00o. we paid $7000 extra in the 1st 90 days and extra every year. It doesn't take a rocket scientist, but there is theft and fraud occurring. Same mortgage amount, less mortgage @ 2.34% rate and no tax increase how is there an escrow shortage every year?