Hi @Pravin Bobade
Is this disassociation due to billing?
If yes, just remove the DDoS protection plan, you can do this by deleting the plan as with the command below:
az network ddos-protection delete --name YourDdosPlanName --resource-group YourResourceGroupName
Now if you just want to make sure that there is no association in the Vnet you can use the command below
az network vnet update --name YourVNetName --resource-group YourResourceGroupName --remove ddosProtectionPlan
In my case there is nothing left after I deleted the vnet.
I did it in my laboratory and I had no problems with having something associated
###DDoS Enable ####
DDoS Plan
Protected Resource
Get in touch if you need more help with this issue. --please don't forget to "[Accept the answer]" if the reply is helpful--