If I use Called Shots and repeat it, can it still be countered by Defy?

Yes, Called Shot can be countered by Defy even if you choose to pay the Repeat cost.

According to the official FAQ #3145 and the game rules regarding Defy:

1. Defy checks Base Cost: Defy only evaluates the printed (base) cost of the spell on the chain. It does not consider any additional costs paid, such as the Repeat cost.
2. Called Shot's Base Cost: Called Shot has a base cost of 0 Energy and 0 Power. Since this is within the target requirements for Defy, it is a legal target.
3. Repeat is not a separate spell: Paying the Repeat cost does not create a second spell on the chain; it modifies the existing spell to execute its instructions a second time upon resolution (Rule 746.1.d).
4. Countering stops the whole effect: When a spell is countered, it does nothing and is placed in the trash (Rule 412.1.a). This stops the entire spell, including both the initial effect and the repeated effect.

Sequence of Events:

• Cast: You place Called Shot on the chain and choose whether to pay the Repeat cost.
• Finalize: The spell is finalized on the chain.
• Respond: Your opponent adds Defy to the chain, targeting Called Shot.
• Resolve: Defy resolves, countering Called Shot. The entire spell (including the repeated portion) is removed from the chain and placed in the trash.

Note: I could not fully verify this ruling against the retrieved rules.