Your friend created an account for you and gave you certain privileges to access his plan. I assume it's still his plan and he's paying the bills etc., so naturally he wouldn't want to give you access to those parts that deal with the plan basics (billing, choice of plan, what privileges, etc.)
You should speak to your friend before you speak to DH support. Maybe he set these privileges by accident; maybe he did so on purpose. Tell your friend what you want to do that you currently can't do, and work from there.
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