|I just bought a TP-LINK router|
Not a bad choice.
|and gave the wi-fi password to some neighbors|
I understand being neighborly, but when it comes to my home network and wi-fied internet I draw the line. I have a couple of guest accounts if I want someone to temporarily use my internet, they have considerable firewalls in place to prevent what happened to you.
I've Ethernet wired it to my internet gateway, along with with two wi-fi extenders that also provide wired hook-ups for my PCs that are in different parts of the house. I have a simple home network and internet access available with the setup. I share files back and forth between the PCs regularly. I also use the wi-fi sharing for internet access for my Fire tablets.
You should be able to reconfigure the IP address of your router, I can easily do it with my Linksys router and wi-fi extenders.
At worst NEVER give someone else you don't trust 100,000% your router's "root" password(s). :)
I've logged more than a few attempts by others trying to get into my network, nope, they ran into a digital brick-wall.
I changed the default IP addresses and passwords as soon as I got the network up and running. That was 6 years ago.
The biggest change was to change from dynamic IP addressing to using static.