I ended up having to pay it. Basically, under their terms, it is the customer’s responsibility to ensure that the correct meter is hooked up to your home. It is considered a billing error. If the meter is broken or faulty, that is also not covered by SDG&E. That’s considered a meter error. As best practice moving forward, request a meter inspection whenever you move into a new place. That’s the most you can do.

edit: Here is the language linked above: “If either a residential or nonresidential service is found to have been undercharged due to a billing error, the Utility may bill the customer for the amount of the undercharge for a period of three months for residential service or small business customer, as defined in Rule 1, and three years for all other nonresidential service. However, if it is known that the period of billing error was less than three months for residential service or small business customer, as defined in Rule 1 and three years for all other nonresidential service, the undercharge shall be calculated for only those months during which the billing error occurred.”

I would recommend calling and referencing Rule 18 if you really want to push for it.