Some suppliers will charge you an exit fee for leaving your contract early but an important note on this — if you apply to leave your old supplier within 49 days of the end of your contract, they are not allowed to charge you any exit fees. You can see a more detailed explanation on the energy regulator OFGEM's website.
If you do think you're still liable for an exit fee, then let us know — you can defer your switch to us by up to a month — just drop us a line to hello@octopus.energy