I think the problem started when you cut them back...
They always say that cutting stuff back is going to produce vigorous growth.
At my house, lantana goes dormant in the winter and stays dormant until Spring...
Winter is when I work on getting new plants.
While lantana grows from cuttings, easier is to propagate by layering.
Your plants have been depleted by the treatment they've received...
I'd be afraid to put them in the basement at this point... What I would suggest... is to get them in a lower temp... + get them more light. I'd want to keep the growth alive + toughen it up... + stop watering so much.
next year... you could try rooting the cuttings, and attempt keeping grown plants in garage or basement...
Oh yeah... stop cutting!
