no power wont charge after drop

Hello,

i recently bought an iphone 6 second hand from a phone shop in the area about 6 months ago. at first the battery drained very quickly so i went back and they replaced it but then it dropped and would t come on unless pressure was applied to the battery against the connector on the motherboard, i recently dropped it once again (not a big fall jus from the bed to the floor) and when i picked it up the screen was black and it had no power and would not charge. i went to the shop i originally brought it from and they tried a new screen and a new battery as well as troubleshooting with no success , they then told me that i should proceed to purchase a new phone because mine was completely dead. i was thinking maybe its the battery connector on the board or maybe a motherboard issue???im confused at this point i just want my iphone to come back on. any help would be greatly appreciated!