I'm a new customer of CertaHosting so given my short time with them (less than a month) its difficult to give a true assessment.
However, I did raise a ticket to investigate an access issues to one of my domains which I made clear I suspected was probably attributable to my ISP but could they check it for me anyway. Their response was fast, professional and courteous for which I'm grateful.
After switching from a host I found unapproachable, rude and on occasion hostile, there attitude and customer service was a breath of fresh air. Very impressed so far and I'm looking forward to a healthy and productive relationship.