threatening sms

good day

kindly assist me, i always receive the sms and email from the company name lifestylelegal Loan tracker SA saying that i am owing them and do not know where did they get my personal details, i havent receive any phone call or documents from them to sign, but they saying i am owing them and they said if i dont pay them they will blacklist me, kindly assist on how can i stop them to sent me sms and emails because i think what they doing is not legal.