False advertising

My little one 7years old needs glasses and her school told me about Specsavers Kids rights to Food sight policy thing. Which I googled and see I had to make a online booking, which I tried but with no luck as all slots are fully booked for 3 months in advance which I can understand. The part I don't understand is the following:

There was no booking spaces available ANYWHERE in North-West, however there's another click here if you need a quicker appointment or something like that. Then all of a sudden there is space available if a parent goes for an eye test as well which cost what....R500???? So in fact this is not a FREE service. There is NOTHING wrong with my eyes yet I have to pay for an eye test just to get a booking for mt child cause for the next 3 months your are fully booked BUT if I pay for myself then there's space available????? Please explain!! I send this exact message to the agent on Whatsapp and this was the reply I got.

Yes, this is correct. Due to the high demand of this offer these timeslots fill up quickly. You have the option to book a joint appointment for you and your child.

I still don't understand if the slots fill up how does it get unfilled when there money involved. I will take my daughter on the 23rd of May 2024 for her eye test and I will not pay for mine as this is false advertising and I hope for everyone's sake that she gets her eyes checked. Thank you.