Did you read the Support and Help Start Here page?
It highlights standard-supported versions of Ubuntu and/or Ubuntu flavors.
Ubuntu 16.04 LTS reached EOSS long ago
Canonical still provide ESM support options, but this is not an appropriate site for ESM support; so if you have an ESM support contract, I suggest using your appropriate method of support.
This is for Ubuntu community support, which covers releases of Ubuntu in standard support only.