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Accelerates transaction with more fee.

Either cancel the transaction, or increase the gas price. I'm not sure you're able to do this with MetaMask, but you could just export your account to another wallet in order to do it.

I think you should just simply cancel the transaction and restart the transaction again

I think there is a heavy congestion in Ether network. There have been notices from many exchanges on this. A very popular Indian exchange has halted Ether transactions with the below notification in their website:

Ether and ERC20 withdrawals update: Ether and ERC20 token withdrawals have been halted due to strong congestion in Ethereum network. Withdrawals will be processed when the congestion clears.