Been billed for one month of membership, however ...

Phone support are the only ones that can help with billing issues.

If you had a renewing membership (of course), the billing date and renewal date are two separate things. Say your Gold membership renewed on the 15th of the month, but your account's billing date is the 5th of the month. If your Gold membership renews on
10/15, then the charge for the 10/15-11/15 term of the membership will process on 11/5. Now, if you disabled autorenew prior to 11/5, then this charge is probably unexpected. However, it is a valid charge.

The add billing info has always been on the free trial. However, you should be able to remove the billing info after you sign up. In regard to using it after signing up for 12 months: There should have also been a terms of service that came up as you were
creating the free trial. Within it, it should state something like: This promotional one time use card cannot be added to an existing Xbox Live gold membership.

generally one month memberships are not refunded that is between you and billing though so call them

however the dashboard cannot turn off autorenewal only the website or by calling support can you do that

as it is turned on everytime you purchase a plan or promotion

I've been with Xbox for only 4 years and have a GS of 8,187, that's roughly 2,046/year or 24,561 in 12 years. I think I'll reach 10,000 by early or mid next year maybe even earlier.

The thing with Tenure is to always renew at least a few days BEFORE it expires, that way it'll keep growing. Microsoft charges very fairly and cheap, for Gold membership. If anyone doubts that, compare 12 months Gold membership to 12 months electricity bill
or 12 months SKY TV bill or 12 months phone/internet bill. Gold membership is waaaaaaayyyyyyyyyyyyyy cheaper than you're average bills.