Malware warning for business site for ATT customers

Hello! ATT visitors to our business website are getting the malware warning. Other visitors have no problem.

We had a previous site on the URL that was attacked, and after trying everything, completely re-built the site and changed domain hosts last year.

Only the ATT customers seem to have this issue on various browsers since then, so it may just need someone to look at it to validate that our page should no longer be on the list.

Our SSL is up-to-date, we have not found any malicious code in diagnostics, and we don't have any third-party plug-ins on our site. 

I would appreciate any help, as this is effecting our small business.

How can we speak to someone about resolving this, or steps we need to take to be whitelisted? 

Thanks in advance!