WHEN WAS BEER-SHEBA NAMED?

Genesis 21:31 Wherefore he (Abraham) called that place Beer-sheba; because there they sware both of them. Genesis 26:33 And he (Isaac) called it Shebah: therefore the name of the city is Beer-sheba unto this day.

Abraham called the PLACE Beer-Sheba, and Isaac named the CITY Beer-Sheba.  Not a contradiction.