Authentication problem with SMTP gateway

I've been sending outgoing email via smtp.comcast.net for years but recently it's been rejecting my connection, sample entry from my mail log

SASL authentication failed; server smtp.comcast.net[96.103.145.180] said: 535 5.7.0 ...authentication rejected (4))

There's no issue with server name, dns resolution or connection, it's just authentication.  I've been trying to get help from the Online Assistant and the Customer Security CSA team which said they would open a ticket and someone with proper access would respond.  It's been a couple of days and no response yet.   What's a proper way to get someone from IT server support team to check my account on the SMTP gateway server?