iirc Silver is added to the account once you sign into D2 on the platform, so you'll likely need to find a way to be able to sign in on an Xbox and load up D2. You may want to fill in a silver ticket [url=https://help.bungie.net/hc/en-us/articles/360049497031-Contact-Form-Missing-Silver]here[/url] ('Submit Request' at the bottom) and explain your situation, include the payment reference thats in the email from Microsoft for the purchase, they'll take a look into it during business hours and see if theres something they can do. If they can't help then you'll likely need access to an Xbox to be able to finish up the Silver being deposited.