Disable IPv6 entirely on a Xiaomi Mi A3

I am running Android One 9 on a Xiaomi Mi A3 and am trying to stop it from using IPv6 DNS servers, as they are essentially turning my RPI4 running Pi-Hole into a useless lump of silicon. How can I do this without having the phone ignore my instructions?? I have tried setting the WiFi connection to use a static IP and DNS info, as well as both the sudo sysctl -w net.ipv6.conf.wlan0.disable_ipv6=1 and the older echo 1 > /proc/sys/net/ipv6/conf/wlan0/disable_ipv6 commands but to no avail...the file retains the value 0 and my phone insists on using one IPv4 and one IPv6 DNS server no matter what I try! Please help me end this madness! MTIA :-)