You've failed to quote a significant part of the regulations:
The Help Assistant (to which you need authenticated access) actually uses email to communicate with customers which makes the refusal to issue MAC codes via the Help Assistant much more significant. PN are selectively ignoring one method of communication to inconvenience/ignore/fob off customers wishing to migrate out. I'll leave it to OFCOM to interpret their own regulations and adjudicate on the matter.
Anyway, people now know how to obtain a MAC code from PlusNet via the Help Assistant if they don't fancy sitting in a phone queue or they're unable to phone during business hours (which most people do). Its just a shame folks have to go to all the bother of sending a complaint to the ISPA to get them moving.
The T&C's used to say you could write in (I can't find this in the current version) and the help assistant says you have to ring in.
PN are infamous for ignoring their own T&Cs when it suits them, but here are those original T&Cs:
26. Notices
26.1 Any party wishing to give notice to the other under this Agreement must use one of the following mechanisms. No other form of communication will be accepted, unless specifically stated otherwise in this agreement:
26.1.1 To us: using the Help Assistant tool at www.plus.net or in writing to:
PlusNet Plc
Internet House
2 Tenter Street
Sheffield
S1 4BY
UK
26.1.2 To you: at the appropriate website using the Help Assistant tool or email to the address provided to you as part of the service or by post to the address provided by you in the Customer Order.
26.2 Any notice given by the Help Assistant tool or by email shall be deemed to be served on the day of transmission. In the case of written postal notice, notice shall be deemed to have been served on the date of acceptance by signature of the recorded delivery or 2 Working Days after the date of posting, whichever is sooner.
26.3 You are responsible for checking for email sent to the email address provided to you as part of the Service.
TT