The color of the line is insignificant. Pregnancy tests can only tell you if you are pregnant. The darkness of the line is no indication of how pregnant you are or how far along you are. You can use the brand tests, even from the same box and get a lighter or darker line any time.
The phantom calls that you have recieved, also known as ghost calls is usually caused by either a poor quality phone line, aka has a high amount of noise or foreign battery due to the line or your on an older copper line.
From Reddit threads to formal studies, obscene phone calls are a known facet of suicide hotline work. In fact, a study conducted by the University of Nottingham found that among hotline volunteers, obscene calls are a major reason for high turnover rate.