Still in Gold live member validity period, but charged again, who can return my money?

Nothing anyone here can do.

For anything billing related you need to contact support
support.xbox.com/.../contact-us

I tried every way to find the right guy to help me, I'm so tired. In china, you should not buy XBOX. I can't get my money back, I can't cancle auto-payment, so it will keep on charge me 65 HDK each month, and 368 HKD each year, ***!!!

Yup, the offer is not valid for existing members. So it's not possible to extend a subscription with the offer.

* Not valid only for existing subscribers. Limit: 1 offer per account; credit card required. Only valid through link in this offer**** SE. From 2/12 to 2/22 new members
buying Xbox Live Gold 1M for $2 will get a second month automatically added to their account at no extra charge. See your next billing date at account.microsoft.com/services.
After promotional period subscription continues to be charged at the then-current regular monthly price (subject to change), unless canceled. Plus applicable taxes.

Hi,

Gold X360 backward compatible games will always show you a Buy This Game.

But, that's no problem, click on Buy This Game and you will see Free if your Gold Subscription is valid. You will also need a valid payment associated to your account.

Excerpt from the FAQ

"When I try to download a game from Xbox.com I get a message that says "You have no valid payment options on file." Will I be charged for the free Games with Gold?

You won’t be charged for the Games with Gold download. The Xbox.com Store requires a valid payment option to download Xbox 360 games. However, no charges will be made since Games with Gold is free to Xbox Live Gold members."

The FAQ can be found here: https://support.xbox.com/en-US/my-account/xbox-live-membership/games-with-gold-faq#c3ca0339eee64eeb90594fd08f34a212

Hope this help

Cheers

Per the terms and conditions, you should receive a code for the 3 months within 2 weeks.

https://www.xbox.com/en-US/promotions/gold-offer

Terms and conditions

*Valid only for non-Gold members who are active on Xbox console and have played a first party shooter game in the past 6 months. Limit: 1 offer per account while supplies last; credit card required. After promotional
period, subscription continues to be charged at the then-current regular monthly price (subject to change) unless cancelled. Plus applicable taxes. Offer not valid on prior Xbox Live Gold purchases and cannot be combined with any other offer. A digital code
valid for 3 months of Xbox Live Gold will be sent to your Xbox Message Center in approximately 2 weeks. Only valid through link in this offer in the US, United Kingdom, France, Germany, Canada, Mexico, Brazil and Australia. (Valid from 10/17 to 10/31)