For issues with free credit offers, you would need to contact the 3rd party you started the offer with. For instance Trial Pay, Peanut Labs, Sponsor Pay, ect. Reaching out to who you bought something from to complete the offer would not help, as they wont have any knowledge of the offer.
It looks like you messaged Member Services who advised you of this and gave you instructions on how to contact these 3rd parties so they could look into this and resolve this issue for you. Unfortunately as the 3rd parties are the only ones that have access to their records for completed offers, our team doesn't have a way to review this for you, which is why they give you the information on how to contact these 3rd parties directly.
Best,
WGTShamWow