My hepatitis c antibody test is non reactive and my signal c/o ratio is 0.01. do they use the signal to cut off ratio even if antibody test is negativ?

Yes: The lab uses a signal to cut off ratio (scr) to try to determine whether a signal is "noise" or real. Your scr is very low, and the lab accurately defined this as a negative response. Note, people can have a high scr and still not have chonic hepatitis c infection. ~25% of people will spontaneously clear hcv after infection. They are left with antibodies but the hcv RNA (viral load) is negative.