Is this my only avenue

After discovering a few calls from my phone to a number I don't know I called MTN for help what did i get, someone is using my phone while I sleep as all the calls are in the middle of the night, my phone is locked with a finger print unlock and its next to my side of the bed i will know if some one has taken my phone. ********** 701 this number is called repeatedly from about 11 and 3. I want to know why i must pay for calls i dont make this number has been reported before and if you Truecaller search it it show check this this...... what is that with no option to report this number. Is my only option to go the police can you not check the number and block it.