AT&T Blocking Websites on my Server

I am looking for some help from an ATT employee please.

I run a static IP, dedicated server, with a professional hosting company. I have many client websites on this server.

Recently I had two different clients inform me they were unable to access their website. I checked and immediately was able to pull up their website.

I did some checking into the issue and learned they were both using ATT on their mobile devices. And they were unable to pull up any website on the server.

I found some spam scripts on the server that were sending out many spam. They were deleted and then we scrubbed the server clean (about 6 hours of work).

I tried to use a new IP Address but was unsuccessful. 

What is the next step? At this time for privacy reasons, I wish to not give specific details publicly. Please message me directly.

Thank you in advance, for your guidance and resolution of this matter.