Permit me to reword this:
"the Church forbids their faithful communicants to communicate with those unbelievers who have forsaken the faith they once received professed . . ."
(These apostates could not have "received" The Faith unto salvation and regeneration, IMHO. Neither were they individually repositories of The Gospel Faith--they were only originally accepted as communicants on the basis of profession.)
Respectfully submitted --
I understand you say this because as an apparent Calvinist you hold to OSAS, but besides that issue and texts to the contrary, we are dealing with RCs here, in which to be faithful to the faith they once received excludes them from salvation unless they repent from such aspects as believing they will finally realize salvation by atoning for sins and becoming good enough in Purgatory. And instead come to God as damned and destitute sinners and cast all their faith on the risen Lord Jesus to save them on His account, by His sinless shed blood.