Faulty charging port

I bought a tablet for my daughter last December and it is still under warranty. 1. First day I returned it to the store as the rubber covering it was faulty and they changed it 2. In April it had a charging problem and we took it in and after collection it was still not working and we returned it fortunately and thankfully it was fixed 3 now it's giving us the same problem we are told it's due to us not charging it correctly.

Now my question is wht is the correct way to charge a phone. As an adult i believe i can handle a phone and charge it The said device is still under warranty. Is this perhaps a way of stalling seeing that the device will soon be out of warranty hence the delay Our household has devices and another bubblegum tablet that is not givinv us issues and this is not the first device we've purchased from them and never had issues Can we really be that stupid and just break a charging port 3 times in a row and do the back and forth of taking it back to be fixed as busy as we are