I took out the option of signing up with no tie-ins so at most a 1 month notice period, so fair point.
However I do think your other point is invalid, as I'm sure that PN would happily put the price up without issuing a new contract if they saw fit, however they have themselves admitted in their forums that they simply didn't bother.
To quote Chris Parr from their forum on 23/7/12
We didn't change existing customers (either direction as there were some exchange that went from Market 2 to Market 1) as it didn't make business sense to do so, if anyone contacted us then we changed the market area but generally we continued charging the price the customer agreed to when they signed up.
And another customer "Gus" in the same thread
Yes you have, since they changed the pricing on market 2 exchanges they have never told us about it. It was a while back when some one posted on usenet that it had changed, day after I told PN my exchange was market 2 and my price dropped by a Fiver on my next bill. But to this day they have never told us the existing customers of the change.
So no new contract is mentioned, merely a drop in the price of the current one which is what I'd expect (but admittedly, not all the information may be in there).
However, my issue is that for 12 months I've been charged more than a new customer would be connecting to the same exchange as me. Even if it was only 10p a month different, it's still not good customer service to just leave it and not tell anyone affected.
plusnet 4/11/2003 -> 4/3/2009 512Kb-2Mb
O2 Standard LLU 4/3/2009 -> 23/6/2009 ~3Mb O2 Access 13/7/2009 -> 22/6/2010 ~8Mb
plusnet 22/6/2010 -> ?? ~8MB