how can i block texts & calls from certain numbers#?

I have a Motorola Moto G 4G v1 on Android 5.1 and am being harrassed by evil family members and cant find how to block anything…i think i found send all calls to voicemail but i want all texts to come through apart from ones i blacklist.

ive tried 5 apps and none worked mostly cos u needed kitkat- others just didnt work at all – its that bad that imm gunna have to get my number changed if not and i have adverts out with my number on etc so would rather not

can anyone PLEASE help me?