The old signallling room only had physical buttons to change the signal and cameras to view the trains passing by, which made it hard to signal at that time.
In The Big Update, the ROC was moved to Benton. The building was left empty since then, and the signalling equipment was removed. It was likely scrapped as the signalling systems at Benton were more high-tech, instead of having physical buttons there are computers.
After the closure of Coxly ROC, the area was still accessible to signallers at first, but later locked off completely. You can still see the entrance to Coxly ROC in Coxly Station, which is located at the front end of Platform 1 behind the signals, but no one can enter the place now.