I bought 3 apple devices. It said I can get one year subscription.for apple tv

I bought 3 apple devices.

Not all devices qualify. It has to be a new iPhone, iPad, iPod touch, Apple TV box, or Mac, as purchased from Apple or an Apple Authorized Reseller.

The offer has to be redeemed on the new Apple device, in the TV app. Apple TV+ - One Year Offer - Apple

The offer has to be redeemed within the first three months. Devices from longer ago do not qualify. Apple TV+ one year offer - Terms and conditions - Apple

I bought 3 apple devices.

The number of devices doesn’t matter. One offer per customer max, regardless of number of devices purchased. Apple TV+ one year offer - Terms and conditions - Apple

seems like they will charge me.

If you accepted the 7 day trial, then you wouldn’t be getting a free year.

If you subscribed before, then you may not be getting a new trial period. The offer is for new subscribers.

If you watched content with an item price tag, then that is not part of the subscription, and that will be billed separately.