Unable to connect to Litecoin Testnet with Litecoin Core on Mac
One possibility is you are using an older version of litecoind which is trying to get testnet3 instead of testnet4.

If this is the case, updating to the latest version should solve it.

See Reset Testnet section at https://blog.litecoin.org/litecoin-core-v0-14-2-release-ab6d2217405f