Neustar Charging DNS data fees after I deleted my account Internet

The Neustar DNS service should be questioned.  I signed up for their basic DNS service over the web and used their services for over a year.  We then deleted some domains from our Neustar account for clients we were no longer servicing. 

We then got a considerable excess data fee.  I reviewed all the domains we had listed with Neustar and all the traffic was within our monthly limits.  

After a few months of email correspondence they worked out the charges were caused by one of our ex clients still pointing their website (that was not hosted)  to Neustar.  

At no time was I warned of excess charges until I received the bill.  

Because I deleted the domain from the Neustar account it was not possible to see the traffic I was charged for.

So I asked them to clarify the following.

I signed up for a DNS service where I can manage ten domains via the Neustar account.  I then later delete the domains from my Neustar account.  I got no warning that I may be charged if a website is pointing to the Neustar service that I do not own or have control over.  Just to clarify the domain deleted from the Neustar account was for a website that was no longer hosted.  I assume it would be common sense that if you delete a domain from the Neustar account that you will stop being charged for that service?

According to Neustar the answer is no.  If you delete a domain from their service you can still  get charged.  I then  proceeded to ask where is that in the terms I agreed to? If I new that I would have not used the Neustar DNS service.   And why was I not warned when deleting domains from  their DNS user account?  No response was received with exception of sending us demand notices.