"I wonder if I can sue Apple Store."
Anyone can sue anyone, but you won't win. Unless the phone repair shop was ALSO an apple store. If they were not, technically what you've done is to replace your charger-port with a non-"Apple original component" by a non-Apple worker.
You can not sue Apple for not doing what unlicensed repairshops are capable of doing. :)
..and void all guarantees as well as functional insurance at the same time. ;)
Also, make sure you don't use the magnetized screwdriver for anything other than to loosen the chassi-screws. For all works inside the phone, you will be needing a "neutral" screwdriver or the components may break.
"Note they say to make the iPhone parts cost well less then £50 but they sell it for £700"
That's only because there are still people on earth that are intellectually deficient enough to buy it. Eradicate those, and the market for cheaply produced but expensively sold goods, will go with them. ;)
Although, there are more costs to the production of electronic consumer items than just the parts. You also need to invest about 100 million dollars on a machine park before you get from Parts to Phone. You need workers that don't kill themselves. You need dis and you need that. Before you know it, the phone may cost up to four times more to producade than you initially calculated. ;)
Welcome to the World of Producers/Production. I hear by your dialect that you've never been here before. ;)
Sorry you had that problem with apple in your country. I had a problem with my Apple desktop computer here in the states. It's been years past the warrantee date but they helped me fix the computer re-did the whole disk drive and did not charge me one single cent. I would suggest you call the main office and report this, or mail a letter to the main American office here in California, USA. This should not happen.