Based on what you described, I would stop repeating the basic troubleshooting and treat this as a warranty/service escalation problem.
Microsoft’s own current Surface documentation says that a Surface can be serviced through a Microsoft service order, and that if a device is returned unserviced because an issue is considered “not covered,” that determination is based on the applicable warranty/protection-plan exclusions.
A few things worth knowing before the steps: all-ports charging failure like this is almost always the charging IC or power delivery circuit on the motherboard — a legitimate hardware defect, not user damage — so it's worth explicitly pushing back on the "not covered" letter rather than accepting it.
Preserve the previous service record.
Don't create a brand-new repair narrative.
Tell Microsoft:
The device was already inspected and submitted for Microsoft service. I dispute the warranty exclusion because the physical condition/reason given in the denial letter does not apply to my device. I want the original warranty determination reviewed by a higher-level Surface support/warranty team.
That's much stronger than simply saying "my Surface won't charge."
Since you've already tried the normal chat/call route, I would try the Microsoft Surface support path through the account/device page rather than starting with generic Windows support:
https://support.microsoft.com/en-us/surface/hardware-warranty/?
https://support.microsoft.com/en-us/surface/service-repair/how-to-get-service-or-repair-for-surface?
DM or reply to @MicrosoftHelps or @Surface with a brief, factual summary and your case number.