The only strict, general entitlement is to take the next available train - which would be the 09:22. Unless this arrives early, you will be delayed by half an hour and will therefore be able to claim back 50% of the cost of your ticket in delay compensation.
In that case the 08:26 is the obvious choice. The 08:26 takes nearly 15 minutes longer to make the journey, too, so it will certainly be 30 minutes late and possibly even the magic 60 minutes, which would mean getting 100% of your fare back.
They are, of course, entirely wrong to purport that they can unilaterally change a contract without compensation or even the courtesy of giving you notice of anticipatory breach.
Delay Repay is based on the contracted arrival time, but you are right that some train companies have been caught refusing to pay out. Keep chasing them and threaten to go to the Ombudsman. Post a new thread for your case if you need any help.
They are legally required to issue a refund on an Advance ticket, if the train is cancelled and the customer chooses not to travel.
I said most because we know some people in this world aren't reasonable. Perhaps I should have said "you are entitled to a refund if"...
The timetables can be (and are) changed at very short notice - late notice / emergency possessions for example. This occurs well after the timetable finalisation (supposedly) at 12 weeks out.
