My headphones have so many issues

I just got these headphones and there are so many problems with it and I’m not sure what to do.

First one is I keep clicking connect then it says connected and disconnecteds and when I click connect again it says connect and again and again never saying disconnected.

Also when I leave my headphones ( complexly off ) the battery goes from 100 percent to 0 very quickly and my battery should be brand new ?

When I charge it that fixes it then when it goes to 80 percent the problem appears for some strange reason but I’m sure you may know about this type of problem I hope I’m not the only one ?

I’ve never over charged or over used these headphones and there brand new and I still have the box please me guidance.

Also if possible I don’t want to buy anything as I don’t have money ( these headphones were a gift from my farther bought directly from you ) “not used”