I just had this same issue (I'm in the US and my rate was showing at 24% when it should have been 0) - and I also wrote to support but got no reply. I did see a couple other threads that explained the tax withholding rate is only validated and shown correctly when you request your first payout:
https://itch.io/t/2033668/tax-withholding-rate-doesnt-change-after-tax-interview
https://itch.io/t/2068276/why-is-my-tax-withholding-rate-still-at-30
I *hated* that I had to proceed with a payout listing incorrect information, but I can confirm that my number did change to 0 when the payout went into processing. I wish I'd had any bit of reassurance - a reply from support or a disclaimer on the dashboard, etc. Since fixing an incorrect tax % is a time sensitive issue, it's a lot to ask new folks to trust strangers in a forum who say the problem fixes itself. But I hope this helps you a little, if you don't hear back from anyone in charge.