Rule 118.11

The actions performed when paying a cost may be modified by effects. Even if they are, meaning the actions that are performed don’t match the actions that are called for, the cost has still been paid. Example: A player controls Psychic Vortex, an enchantment with a cumulative upkeep cost of “Draw a card,” and Obstinate Familiar, a creature that says “If you would draw a card, you may skip that draw instead.” The player may decide to pay Psychic Vortex’s cumulative upkeep cost and then draw no cards instead of drawing the appropriate amount. The cumulative upkeep cost has still been paid.