How do you block a call on a samsung sgh-a837

You can try to use LEO Privacy to block unwanted calls, there is a Harassment Intercept feature in LEO Privacy. You can add unwanted calls into black list of LEO Privacy. LEO Privacy Applock Hide Safe Android Apps on Google Play

Go to the settings then on that go to call settings on that click call block settings then add a number and switch on the block options. You can do it simple by when some person call you open call histoy and on the number of which you need to block select it and go to option and click on the block option on it