Static IP address changed after using it for 3 years

My static IP of 3 years was replaced with a completely different one yesturday. My original started with 75 now this new one is 96. I called comcast and said that this has been my static since the start of me purchasing it. I just remoted into my server yesturday morning via RDP with the 75 but in the afternoon the modem went "bad" and would let me connect. Comcast said that this IP was used on a different account. I am incredibly frusterated and need answers because comcast buisness support know nothing and neither do their supervisors.