@Aka414 the phone number I have for Deniz is 905314590933. Like most people there, they are active on Whatsapp; a regular text went unanswered, but via Whatsapp he was very responsive.
A note on how this particular operation worked: you'll communicate with the guy who is their arranger; he will set up (depending on your requirements and preferences) both a driver and a tour guide. The driver may or may not speak any English, but the tour guide (Omer, in our case) was fantastic, both in language and knowledge. Their Mercedes busses were immaculate, modern, and comfortable.
In our case, the main guy (with whom we had been communicating) and his driver met us outside the cruise terminal, on the sidewalk. He confirmed a few things, introduced us to the driver, then he was done, and we didn't see him again. The driver (who spoke decent English) took us up the central area we wanted (Hagia Sophia, Blue Mosque, Cisterns all in a central area); he took us to the tour guide, introduced us, then the driver departed. After the tour was over, the tour guide called a different driver, who arrived and took us to OUR chosen dinner spot; he didn't speak any English, but he used Google Translate and it was surprisingly effective (mostly he asked yes/no questions, so that helped). I must stress how anxious and focused that driver was on getting us to our chosen dinner restaurant (there are apparently several locations in town); he had a good heart and wanted our trip to be perfect.
If my contact info for Deniz doesn't work out for you, let me know. I don't recall specifically, but I think our total (not including the food) was about $170 US. This was a private tour, just the two of us.