"Receptionist was so rude, it was uncalled for"

I have been unwell since last week, having episodes of dizziness, fatigue, blurry vision etc. I informed my work that I am unable to attend my duties due to being unwell, they asked for a sick note. I called 111 last night as my symptoms had worsened and the out of hours GP sent a note in my doctors surgery explaining my illness and to grant me a sick note. I called Riverside Health Centre this morning to confirm this had been done and was put through to a receptionist who was rude from the get go. I explained my situation to which they said the out of hours GP is not a doctor and I have to be seen by one of theirs. I asked to be given an appointment to which they said I have to use their online form, this can only be used for 15 minutes after 8am and then it closes. The receptionist was so rude, it was uncalled for. I suffer with mental health and situations like this make it worse. They did not need to speak to me in such a condescending tone.