I didn't know Zen did High/Low cost areas, except that ADSL Max (20CN) I seem to remember is more expensive than 21CN.
High/Low cost is normally based on the Ofcom Market Classification. These used to be 1, 2 and 3. Changed recently to A/B. But it is nothing at all to do with whether the BT Wholesale provision is 20CN or 21CN.
Ofcom basically classified them on the basis of the number of providers other than BT Wholesale. Typically Sky/TalkTalk/C& W LLU and Virgin Media cable.
However Zen over the last few years have introduced a number of POPs. (Points of Presence). That means they can provide a better and less costly (to them) service - AIUI it still uses the BT Wholesale MSANs but not the BT Wholesale WBC backhaul.
What has happened with your connection seems very odd. BT Wholesale 21CN costs them less than 20CN anyway! If it is one of their POP-linked exchanges, (Samknows shows Zen in the LLU column if it is, that's if sam is up to date), it should be cheaper still. I wonder if whoever told you it was a high cost area is confused? On 20CN it would be, but it is now 21CN.
The indispensable man or woman passes from the scene, and what happens next is more or less the same thing as was happening before.
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