WBC (Wholesale Broadband Connect) and WBMC (Wholesale Broadband Managed Connect) are and always were the two ADSL2+ services available to ISPs from BT Wholesale. Nothing has changed in that respect.
What you may have experienced is a move from either Zen's own backhaul, or don't they also use TalkTalk Business for some as well. I'm not sure about the latter.
My broadband basic info/help site - www.robertos.me.uk.
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