@MartasCZR 

Check your Internet port negotioatiated speed:

If it's 100 Mbps the that's the reason - it should be 1000 Mbps to be able to get more than 100 Mbps trafffic from your ISP. Use a different ethernet cable (Cat 5e/Cat 6) or if that persists change this setting and test again:

I tried to do that but its still same.

@MartasCZR 

What do you mean by "its still the same" ? What's your Internet port negotiated speed right now ? (refer my first screenshot)

Its still gives me a 100mbps even if i tried to change it manually i think the isp connector is broken, because i talked to technician of isp and they told me to try another router and the negrogation was the same even on asus, i tried to connect tp-link to asus and when i connect it it shows 1gbps. He will come in the evening to take a look of the connector from the wall.

I hope they do.