Samsung Galaxy J7 Prime mobile phone - problematic after repairs

Good day

i got a Samsung Galaxy J7 Prime mobile phone through Telkom in March 2018. I sent my phone in for repairs a month ago as the screen was jumping and i couldn't a lot of the time write a message on whatsapp as my text was cancelled as i was writing a message. i had to wait 21 days to get my phone back after repairs and now whilst having it for a week, the same problem is starting, so clearly the problem has not being fixed. My phone is new yet it feels like a old phone, very problematic. How can the repairs department work like this??? im disgusted. Is the repairs department not competent enough??? how many times will i have to repair my phone in order to be happy?