Hello, polygon is unstable. You can switch the ETH chain and polygon chain in metamask continuously to restore the matic on polygon to normal, and then proceed with the following operations.
Would you please submit a help desk ticket through the live support feature at support.metamask.io ?
Click the blue ‘start a conversation;’ (example image below). It will first connect you to a bot but as you answer the questions it will file a support ticket. Remember that nobody, including from support should ever ask for your secret recovery phrase. you should never provide it to anyone and also never input it on a site or pop-up window to confirm it.