I'm in the same situation. Trying to get a last minute cruise for March 6 Divina cruise and the MSC site is a nightmare and the 2 TAs I spoke to don't work with them. Interior cabins seem to come and go nearly hourly. I searched online for some referrals but nogo. The one TA that I found so far that does work with them actually was showing me a worse deal than MSC direct.
It should not be this hard. I've read the MSC has a new staff member that has pledged to resolve these issues and they are investing in improvements to booking, but not soon enough for me.
I guess Princess and NCL left me with a false sense of ease as they were much easier to deal with direct.