Board Thread:Support Requests - Community Management/@comment-28589934-20151103055936/@comment-1647694-20151103061036

The admin must of had the "Automatically block the last IP address used by this user, and any subsequent IPs they try to edit from" box checked which would have blocked your old account and your IP address. When they removed the block on your old account they did not remove the IP block.

For you so be able to use your account again the admin will need to remove the IP block which will look something like Autoblock #12345 in the Special:BlockList.

See also: Help:Blocking