Uc overpayment

Hope some one can point me in right direction. In covid I applied for uc and was awarded it. Stopped claiming further down year. In 2023 I was told that I wasn't entitled to what I had claimed. Reason was because I forgot to send proof of who I was and a copy of my lease. I have memory problems and chronic illnesses Seen CAB which weren't that great, they sent letter from gp etc, got vague reply and cab got no response their responding letter. Fast forward became of pensionable age this March, received one full payment, next moth they took off almost half my pension, I'm self employed, just living from month to month, I'm going to have to vastly reduce what I work due to health issues. There was no negotiation they just did it. What if anything can I do? Mentally not in a good place over thus

Thank you, I've already had a look at those but only cover England, I forgot to say I'm in Scotland and keep getting bounced around