I have been getting a monthly charge for ultimate month 1 for months for $19.99. I do not...

Typically this would mean your credit card number is compromised and you should contact your bank

You have fo check account.Microsoft.com ir on you console and subscription

The 18 dollar charge sounds like you upgraded to ultimate if monthly

But that would've been after your upgraded time

When adding ultimate it upgrades your time at 3:2 ratio so8 months for every year of gold plus the 1 month of ultimate for 9 months of ultimate

Yes. You buy the 1 month of Ultimate and it'll convert your 12 months of Gold as well, so you'll end up with 13 months of Ultimate. You'll be charged monthly for Ultimate after the 13 months if you do not turn off auto-renewal before then or extend the time with prepaid cards.

If you already have Core and you upgrade to Ultimate, you will be charged for 1 month of Ultimate immediately whoch is added onto the Core you already have that is being converted. The monthly charge won't start until after all of that time expires. So for example, 3 months of Core converts to 2 months of Ultimate. If you add the 3 months of Core, then buy 1 month of Ultimate, you should end up with a total of 3 months of Ultimate. You won't pay again until those 3 months are up.

The 6 months you have left will convert to Ultimate plus you'll have the time you purchase. So of you're buying 1 month of Ultimate, you will have 7 months total and will not have to pay again until after the 7 months. After that you will be charged monthly.