To be able to complete the upgrade of an iLok license, your new upgrade license must be deposited in the same iLok account where your old license being upgraded can be found.
You can see the surrender process in this iLok video:
If you deposit your new upgrade license in a different iLok account, your old license will not be found, and you will not be able to complete your upgrade.
To resolve this problem, you can transfer your old license being upgraded from the iLok account where it is found to the iLok account where you deposited you new upgrade license - normally you can do this immediately, following the steps indicated in this article: How do I transfer my license to another iLok account?
If necessary, you can open a Support ticket to request assistance with this issue.