Miraculous technician... shady handling fee policy!

Got a phone - it wouldnt charge fully. Returned it within 7days, store confirmed it wasnt charging and asked me to leave it with them o their technician could 'charge it' and check the settings (*******!). I was told since it was the 7th day, if I dont leave it with them, then I dont qualify for a swop because it would be day 8 when I return it. Miraculously, it charged when the technician charged it in my absence. When I was in the store, we watched it not charge as expected for almost 30minutes. Now I dont want it and they want me to pay a handling fee because I didnt return it in its original packaging. In their terms, this means the box was opened. Im sorry - this is very shady behaviour!