When I change the MQTT setting on my bridge, I use enabled (with a d at the end), not enable as suggested above. The API Docs also say the name of the setting is “enabled”.
So the command would be:
curl -i http://< bridge >/v2/api/mqtt -H "BOND-Token: < token >" -X PATCH -d '{"enabled": false}'
After changing the setting, the bridge should also be rebooted:
curl -i http://< bridge >/v2/sys/reboot -X PUT -d '{"_token": "< token >"}' --max-time 5