Very disappointing method of increasing prices

I have today received an email form Octopus increasing my electricity payment by almost 50%. I am currently in debit by (according to Octopus £7.15, but according to the atual bills they have sent me £2.92). Octopus however wish to increase my payments from £65 per month to almost £90. This is to "help me manage my balance". I take exception to this for a number of reasons. Firstly I am a tiny amount in debit. Octopus have previously assured me this is normal for "this time of year". Secondly, they have not published the actual price increases to me, so this looks to be, at best, an estimate.. Thirdly, Octopus seem to like and, indeed, encourage the customer to mange their account and payments etc. However, in this instance they have chosen a rather bullying route to make extra money. Traditionally one pays for the electricity one has used and is not expected to pay "in advance" to help maximise a companies' profits (imagine sitting in a restaurant and being given the bill before ordering "lest you eat more that you thought you might", one would not accept that situation).

I will, of course, be looking to change my supplier from Octopus with immediacy.