Focus on things. Actual things. Try to describe things simply, directly, and in natural language first.
Then, when you ask for design guidance, you can provide definitions. In some cases, the act of writing definitions will make the design crystalize.
Orders are things. What are the attributes of an order? Customer, Product, Payment/Billing options.
Billing Options are (almost) things. You can, apparently, define and identify them. (I'm not sure I could. From your question, it appears that you might be able to. But without a one-sentence summary, I'm not sure what's going on with Billion Options.
What's a "billing data?" What kind of thing is this? What attributes (or properties) does it have?
How does a "Billing Data" relate to an Order? How does it relate to a Billing Option?
Feel free to update the question with definitions for each thing.
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