cannot find old connection string connecting to old database and not new one that has been defined
To add on to what Max is saying, you could use the following to get you the sql info and use the port information and sql text to figure out which service is doing what and then use those additional clues to help you isolate where it's coming from.

SELECT 
   des.host_name
    , des.program_name
    , des.login_name
    , dec.client_net_address
    , dec.client_tcp_port
    , db_name(a.dbid) as db_name
    , object_name(a.objectid) as object_name
    , a.text as sql_text
FROM sys.dm_exec_sessions des
    INNER JOIN sys.dm_exec_connections dec ON des.session_id = dec.session_id
    CROSS APPLY sys.dm_exec_sql_text(most_recent_sql_handle) a
WHERE des.is_user_process = 1;