It's a well-known and stupid problem, which can hit even when there is availability letting you order. I can only think it is that it simply isn't catered for in the Openreach ordering system
. Either a design or coding omission, or a bug.
In your case the fact there is no availabilty stops you ordering which is daft, but does at least mean you still have the service.
If you were able to order and say there was only one spare port then although we were recently told a port is allocated at order time this doesn't seem foolproof. We have seen many where the migration starts, the current FTTC gets released, there is no spare port (which shouldn't matter because on a migration the port doesn't change), but the top order on the waiting list has snaffled the one the customer was on in between the the release and reuse. The migrator ends up at the bottom of the waiting list, not even the top.
Madness. Presumably the "remote from cabinet" end gets disconnected to switch the routing to the new ISP, and that's where the problem arises. Not at the physical port in the cabinet, but at the one in the exchange.
Somebody in the depths of Openreach might know, or maybe management is blissfully unaware there is a problem, or just doesn't care. It works as far as they are concerned, with maximum utilisation and cash flow.
In the case of BT Consumer, which is BT Retail broadband, AIUI they don't even use the the waiting list for users ordering from them, so those caught by this end up on ADSL2+ at best and an upgrade order has to be placed.
The tiny bit of good news is that if you post your exchsnge and cabinet number there are a few people on the forum who can tell you if there are plans to increase your cabinet's capacity, and maybe when.
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