Why won't my phone stay in sleep mode after I lock it?

[AC Question]

So I have a Samsung J5. It had suffered some damage so I sent it to my insurance co. to get it repaired. Now I have got it back, every time I go to lock it, my screen comes back on again and when it tries to go into sleep mode again it just turns itself back on. This is a problem I really need to fix because it's draining my battery and I use my phone for work. What can I do?