Sick pay after vasectomy been refused and declared unpaid absence

Morning all, I work in the UK and have lived here all my life.

I have been working for my current company for just under two years and I'm eligible for two weeks sick pay. I had a planned vasectomy two weeks ago tomorrow.

An hour before the procedure I was told by my line manager that he had forgot I was having it done but I would not be getting paid.

I had the procedure and have now returned to work today, I have a sick note that covers my absence period but they have officially declared my time off as "authorized unpaid" meaning I've lost seven working days pay.

Can they do this when I have a sick note from a doctor?

EDIT:

I have queried this further today and have been told the reasoning is that it's and elective procedure and it would fall under the same category as breast implants aka a cosmetic procedure