Welcome @Pepe to the MetaMask community.
Are you able to see this transaction on a block explorer such as https://polygonscan.com/?
Was your ETH on Eth mainnet or the Matic network? Usually the network wouldn’t change during the transaction. Happy to take a deeper look, for security reasons, please open a support ticket here with your wallet’s public address and transaction ID for the transfer in question. https://metamask.zendesk.com/hc/en-us
Be aware of scammers and not share your seed phrase-secret recovery phrase.