[BUG] Can't upgrade Max 5x → Max 20x: payment fails on every attempt, support unresponsive

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Every attempt to upgrade from Max 5x to Max 20x fails with a payment error. This has been ongoing for 3+ days.

Tried multiple cards — all fail with the same error
Banks confirm no decline is happening on their end
The error is server-side, within Anthropic's payment flow (Stripe)
Existing Max 5x subscription and all previous payments work fine — this is isolated to the plan upgrade flow

Support attempts (all failed):

Fin AI Agent (in-app support): Bot suggested checking "Why was my card declined" FAQ — completely irrelevant since banks confirm no decline. When I requested escalation to a human agent, Fin closed the conversation with "This conversation has been closed and is no longer monitored."
Email to support: No response
Twitter/X (@AnthropicAI): No response

A paying customer on a $100/month plan is unable to upgrade to a $200/month plan, and there is no functional path to reach a human for resolution. This is a billing-system issue on Anthropic's side, not a card/bank issue.
This is a known issue affecting multiple users, particularly in India and other international regions. See also:

#55917 (Pro → Max upgrade failure, India)
#45361 (API credits purchase failure, Italy — 3DS passes but Stripe declines)
#50710 (Subscription stuck in broken state after card expiry)
#10832 (Max20 subscription not updating after upgrade)

What Should Happen?

Payment should process and subscription should upgrade from Max 5x to Max 20x.

Error Messages/Logs

Steps to Reproduce

Log into claude.ai with an active Max 5x subscription
Navigate to Settings → Billing
Attempt to upgrade to Max 20x
Enter card details (any card — multiple tested)
Payment fails with authentication/processing error/Timeout Error
Try different cards, browsers, incognito mode — same result
Contact support — get looped by AI bot, then conversation closed

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

na

Platform

Other

Operating System

Windows

Terminal/Shell

Other

Additional Information

Fin AI agent closed the conversation after being asked to forward to a human agent, with no escalation and no ticket number.
This issue is filed on the Claude Code repo because it is the only Anthropic GitHub repository that appears to be actively monitored. There is no dedicated billing/platform repo for claude.ai issues.
Impact: Paying customer unable to upgrade. Actively considering switching to competitor (OpenAI Codex) due to combined billing failure + zero support access. This represents direct revenue loss for Anthropic.