Has my old iphone been erased?

So i had an iphone 4s that decided not to turn on anymore, was completely broke and managed to get an early upgrade. I'm not an expert so wasn't aware i could erase my stuff from a pc. I have icloud and signed in on my new iphone with the same email, and put my stuff on that phone.

has it been erased from my old phone which doesn't turn on? I can't tell obviously as it doesn't turn on and yes i tried everything, think its a problem with the motherboard.

my icloud, only detects one phone (new one) when i go on find my iphone.

i'm asking as i want to return my old iphone to the shop for a discount on what i owe o2 but want all my stuff removed as i had personal info/

so will it still be on there or not?

No all your stuff will be on there. The best you can try to do is plug it into itunes and try to restore it to factory settings but i'm unsure that will work considering the condition of the phone.