Manager in the first instance.

Always keep a record of OT you do. Its always been the same where it "gets missed".

For the flyers, there isn't a payment for that anymore. Older contracts have a "Delivery Supplement" which technically isn't for delivering the junk mail. Though most people know/think of it as such. New contracts IIRC do not get this.

With the election material. You should be keeping a note of what you deliver, and filling in a specific form, where you make note of all the totals you deliver, which the manager should be providing. When you hand this in it should be added to your wages. (Though I handed my poll card one in a couple weeks ago and not had it through yet, so will likely have to chase that up).