Lexus Forum - Lexus Enthusiast Forums - No Volume Control.. HELLLPPP

So a few weeks ago i lost volume control in my 2015 IS 350 with the mark levinson sound system.. I took to lexus they thought was amp but werent sure, I went to a local car audio shop and they said it was amp.. So i bought a refurbished amp online and just installed it.. Still no volume control... I called the gtuy who sold me amp and he went over a few tests with me using multimeter on the amp connection cables and everything tested out fine..

Im lost at what to do.. my next guess would be head unit, but everything else on the head unit works.. all the other switches and everything are good.. i dk what else the issue could be... Can anyone help me??