1st call goes straight to voicemail, 2nd call goes through

When others call me, the first call always goes straight to voice mail while the second call would go through. This happens regardless of whether they're in my contact list or not. After the second call goes through, if you wait like 5-10 minutes and call me again, it'd go back to being the first call and won't go through. There's nothing wrong with my service since I share a package with my family and their phones are all fine. I tried restarting but it didn't work.