Requesting the money back is an interesting one, because you can argue that it was what had been advertised.
Back when digital cameras were coming down to consumer pricing, Kodak made a mistake on their website. A 3.1 megapixel camera (posh for the time), docking station, memory card and some printer paper all for £100. I think it was usually £400 and they had a £100 reduction. Someone made a mistake. Quite a lot of people signed up (Becs tipped me off), Kodak said no, some started legal action as we had a contract of sale. Eventually Kodak caved and I got a camera.
I think following that one the law was changed to say the online agreed price had to stay, even if it was a mistake. It feels like a pension payout should be the same. If someone is given a certain amount and told they had earned that amount then I don't think you should be able to recall it and for future payments the pension company has to give reasonable notice of the change of payments, say 6-12 months.
People plan their lives on this. If the pension company makes that mistake then they own the responsibility for that mistake. If they can demand repayment and apply penalties, that means the responsibility for their mistake lies with the customer. That is wrong.
Pensions are complicated. I like to think I'm intelligent, good with maths and quite like a spreadsheet. It took me a lot of study and experimentation to fully understand my pension. In the process, I found the pension companies own modelling tool was wrong, where it calculated pension earned on a weekly basis and rounded down at each step. The cumulative effect was a few thousand out over a 15 year period. If they can't get it right, and the documentation is complicated, what hope does the average customer have?