Does Defy cancel a repeated spell in its entirety if the repeat cost was paid for?

Yes, Defy cancels the entire spell, including the repeated portion, if the Repeat cost was paid.

According to FAQ #256 and FAQ #658, when you cast a spell with Repeat, you must choose whether to pay the Repeat cost as an additional cost before the spell is finalized onto the chain. Once finalized, the spell (including any Repeat) exists as a single entity on the chain. If your opponent uses Defy on that spell, the entire spell is countered, and none of its effects occur.

Key points regarding this interaction:

• Single Spell: Repeat does not create a second spell; it extends the effect box of the original spell so that it executes its instructions multiple times.
• No Partial Countering: Because it is a single spell on the chain, Defy counters the entire object. You cannot "save" the repeated portion if the base spell is countered.
• Cost Check: Defy only checks the printed cost of the card, not the total cost paid (including the Repeat cost). Even if you paid extra for Repeat, the spell remains a valid target for Defy if its printed cost meets the criteria.
• No Refunds: As stated in Rule 412.1.c, countering a card does not refund any costs paid to play it, including additional costs like Repeat.