Unable to update personal details!

I’ve been trying to change my address, so it is correct on my bank statement, which I need to show, as additional prove of address. This as been going on for other a year. Ive been into branch, 3 times in regards to this and on the phone twice, both not short times. Being move from 1 department to another. They have my correct address, but on ever bank statement, invoice or correspondence, has my old address, not my present one. For such a simple thing, I can’t believe to is proving so difficult.