unable to get gp authorization on weekends.

why is that every time my dad goes to a gp on a weekend they are unable to get authorization and my dad needs to pay cash. this is highly inconvenient as my dad only gets a government pension and does not have cash to just take out anytime.. my dad went to dr r rugnath on the 19/03/2022 and was told he needs to pay cash because bonitas is closed on weekends and the gp does not issue receipts for some reason for me to submit a claim. its just their rule. now when i call the surgery their phone is on engaged tone. please help fix this and get my claim through and get my refund from the doctor.