Fashionista1
My pension was calculated incorrectly as I retired. I had paid more contributions than DWP gave credit for. Luckily I had kept every pay slip I had ever had and eventually DWP conceded that I was entitled to more pension than had been calculated originally. It took time to sort out but I now have the correct pension for the rest of my life it was well worth pursuing. Just a warning to you all that they don't always get it right.
I had the opposite when my mother died. It turned out that - entirely due to DWP's mistake - she'd been overpaid for years.
Even though it was their fault the estate still had to pay it back.