The domain still has the nameservers NS1.VOXDNS.CO.ZA and NS2.VOXDNS.CO.ZA, that’s why it’s not activating in Cloudflare.
It seems you added the two Cloudflare nameservers hans.ns.cloudflare.com and arya.ns.cloudflare.com as NS records to your current DNS provider. But that’s not the correct thing to make Cloudflare the authoritative DNS provider.
You should instead replace the current nameservers with two Cloudflare nameservers in your domain registration panel.
I have replaced the old records with the new ones and can see the propagation working mostly around the globe. The ISP has verified that the records are changed on their side and that DNSSEC is disabled.
Other than your ISP “verifying”, have you done so yourself? What exactly did you check for, and can you share the result here? (NB: Hopefully you’re not using a tool that’s doing a simple NS record lookup!)
A simple lookup for your domain spier.co.za at the .za Registry – the ultimate source of truth for .za domains – shows the domain still has VOXDNS nameservers. Check for yourself here: https://registry.net.za/whois/