Likely you are not connected to the POA network.Ethereum and POA Network externally owned addresses can co-exist on multiple chains. Switch the network to Mainnet to see tokens on Ethereum, and switch to POA Network to see tokens on POA (or xDai to see your balances on the xDai chain).To switch networks in MetaMask, click on the Network dropdown to select. Note that POA and xDai are not native to MetaMask, so you will need to add them as custom networks. Instructions are below.