Hearing two beeps before calls/not getting some calls

I have a I-Phone 6 plus and everything has been amazing with the phone. Just recently I moved to my new apartment and have been having issues with making/receiving calls. My girlfriend will try to call me and receive a busy tone or get sent to voicemail immediately. When I am making a call it will sometimes beep twice then the dial tone will come on. Also my apartment complex has a gate code that is to be pressed and then calls my phone to let people in, but have not received anything from the system. I have tried with other peoples numbers and works fine. I went to my service provider (Sprint) and they had no answer for me. Said it couldn't have anything to do with the service. Thinking about hard resetting my phone but would prefer not to. If I could get some help that would be great.