Tfg card harassment

Since I bought bought a Redmi 14 c at Markhams Wonderboom ony tfg account I continue receiving non ending calls from tfg connect regarding data and airtime on a tfg SIM card. The guy at Markhams said I had to purchase a tfg SIM card as it will affect the phones warranty. I have blocked numbers but now they keep on calling from different numbers. I already told them I have a contract which has data and airtime. This is called harassment. Can't they get the message i am not interested. Enough is enough.