Deleting versions with null ID

I have been trying to delete versions from a bucket which has null version ID set as the versioning was on before and then we suspended the versioning in between. 

I have tried deleting the version through S3API

aws --endpoint-url <<endpoint>> s3api delete-object --bucket <<bucketname>>  --key "<<object_key>>"   --version-id null

It shows output as:

{
    "VersionId": "0"
}

But it is not actually deleted.

And because of this when I try to delete the bucket from ECS Web UI portal it shows "Bucket Deletion in Progress" but actually fails to delete the bucket.

My purpose here is to delete the whole bucket itself and hence I am trying to clear the versions from it. Please assist.