After all the finagling involved to get a home loan in the first place, you’d think your lender would just stick with the payment the two of you agreed on. But things can change with your mortgage. And when they do, your payment changes with them. Of course, your lender might have made a mistake, but that’s by far the least likely possibility. Before you make calls demanding a correction, look at these four situations that could trigger a different mortgage payment amount for you this month:

Your adjustable rate mortgage got adjusted

If you’re unclear on how ARMs work, now is a great time to ask for an explanation and see if there’s any advantage to switching to a fixed-rate mortgage at some point in the future.

Your homeowner’s insurance or property tax costs more

If your lender pays for these expenses out of an escrow account, any time the rates for either one increases so does your mortgage payment. The bill should break out what you’re paying for escrow expenses, so that should be an easy one to recognize

Your private mortgage insurance is done

This would be one of those pleasant surprise cuts in your monthly mortgage amount. Once you reach a certain equity level in the house, you no longer are required to keep a private mortgage insurance policy.

You’re paying some new fee

Review all your recent correspondence from your servicer to see if they notified you of some fee that would increase your payment.

According to the Federal Consumer Financial Protection Bureau, if you’re still left with questions after considering all these potential explanations, you should contact your lender for an explanation. Make sure you take notes for your records and ask for the name and job title of whoever fields your phone call. If they really did charge you too much, you’ll want a paper trail to help you correct the situation.