The Support Center is the dedicated resource for clients to get help with account and billing issues, such as unexpected charges on their statement. Here, they can open a case to receive direct assistance. While the other options mentioned have their purposes, they do not offer the direct billing-issue resolution service that the Support Center does.

Consulting general guides or documentation provides only broad information on service costs and pricing structures, without the ability to address individual account concerns. The cost optimization service offers advice on reducing expenses but isn't meant for inquiry into specific billing charges. The pricing estimation tool is for prospective cost assessments before deploying services, not for examining existing account charges.