Can I use a 12months Xbox live subscription code while midway though a Gold subscription?

You can stack Xbox Live Gold time for up to 3 years. The 12 months will be added to whatever you already have left.

I didn't receive a code either and have purchased a 12month gold subscription.

http://support.xbox.com/billing/xbox-subscriptions/trial-gold-subscription

The following limitations and restrictions apply to Xbox Live trial subscriptions from games or console bundles:

• If you have an existing paid Xbox Live Gold subscription, you can’t redeem Xbox Live Gold trial subscriptions from games or console bundles to extend your subscription period. However, you can redeem the prepaid code once your current paid subscription
  expires.
• Prepaid codes for Xbox Live Gold trial subscriptions are only available in select games and bundles.
• You can’t access Games with Gold for the Xbox 360 with this type of Xbox Live Gold trial subscription.
• You can’t stack prepaid codes for Xbox Live Gold trial subscriptions from games or console bundles. This means that you can’t start another trial period before your current trial period has finished. However, you can purchase a new paid Xbox Live Gold subscription
  and start the subscription at any time during the trial period.
• If you don’t currently have a paid Xbox Live Gold subscription, there is no limit to the number of times you can use this type of Xbox Live Gold trial subscription.

Xbox Live Gold subscriptions can come from Prepaid Codes, which when redeemed will expire at the end of term, or from a recurring subscription purchase via a payment method (credit/debit/paypal)... currently, aside from promotions, you can either purchase
a 1 month, 3month, 12month, or 12month Family Pack...

Cancelling the card will not cancel the subscription, and if you do not turn off the automatic renewal, it will attempt to charge and your account will go into decline with a past due balance...

Also, you can not remove the payment option from your account so long as there is a current subscription attached to that card, whether it is set to renew or not... so in this case, you will need to call Xbox Support so they cancel the subscription, remove
your card, and then provide you with your remaining time...

No, That is not what i want to do, Or trying to do!

My 12month subscription was bought with my sisters credit card, But she just recently got a new credit card. So the credit card that my 12month subscription is under is no longer in use. So my question is, Should i edit my payment options and add the new
credit card info for my 12month live subscription? Because right now my 12month sunscription is under her old credit card that is no longer in use.

But i also have auto renuall OFF, But is it okay it i just continue to use my 12 months with the old card info in my xbox? I dont buy anything with it, It's only for my 12months gold. So should i just let it expire than change the card into with the new
card?