Employee asking for attendance letter (England)

Hello! Back in December I attended the walk in centre due to a chest infection

ETA: I was off sick for 6 working days plus 2 off days so 8 days

Now my employer is pestering me about an attendance letter for that day. I will have a sick note that should prove I was there but my employer won’t leave me alone now about the attendance letter

What can I do? Do I still need to give them the attendance letter or not?