When she dumped you and forced you to leave your own home and demanded the only communication you have is about the children she lost all rights to talk/vent her problems or issues to you.
Instead of setting boundaries you make it about "cutting her off" which is not the kind way to detach. Again, all the focus goes back to your W. You think she had any focus on you when she was prancing around Florida with OM? You think she had any focus on you when she was riding bikes and playing with guns with older OM? No.
When she needs to vent about her crazy family or money she calls you. When she needs a favor she calls you. And you let her. So don't complain because you CAN stop this but you DONT.
Venting is not a sign of anything other than her knowing she can talk your ear off when it suits her. I bet you 20.00 if you had a problem with YOUR family at 9pm on a Sat. night when she was headed out for the evening she wouldn't even take your call.