How to I contact Engineering ? Naples, Florida

Without going into much detail I have a Gigabit plan but the fastest download speeds I've received the past 2 months with a direct ethernet connection is between 80 and 90 mbps .   Using Wifi 5 to 10 feet away varies from 20 to 50 mbps on 2 smartphones and an Ipad  .   Upload varies from 15 to 30 mbps and I noticed that the modem is using only 2 of the 4 channels .   The modem is a Motorola 8611 and the router is Motorola AC2600 .   

In the last month I've had techs come to my house on 3 occasions .  After the second visit they  indicated that there a problem with the system in some sections of my community .  This was after I switched modems because they said the modem was the problem .   After the second tech visit I rceived a text that the system was fixed .  It wasn't . 

After the third visit the tech told me that engineering would be in contact with me .  That was on January 3rd and over 3 weeks later the same slow speeds and no communication from engineering or anyone from Comcast .   

Calling tech support as I have on numerous occasions is diving into an abyss .    I pay for giga and Xfinity gives me DSL speeds . 

So how do I get the attention of Comcast or reach engineering ?