As far as I’m aware from a family member with a similar situation they need to prove they aren’t fit for work with a sick note from the go. Likely the old one had a time period or perhaps they think they are ready for work now. They need proof from a medical professional that They are unable to do any type of work. My family member was not given a new note as the gp believed they were fit to work, maybe not their original occupation but a job none the less. They were knocked of the sick and had to sign up for UC and look for a job. It’s essential a review of their claim to see if they’re eligible and if they aren’t payments will be stopped ASAP