Connection failed error on Kubuntu 18.04 when updating and upgrading

Before all, i am sorry if this problem is asked a lot already. I tried the solutions available in other’s thread and nothing just work for me. Also, i’m really new at linux (just installed kubuntu yesteday) so i may trip over a little thing a lot.

So, my problem is when i do anything related to update, upgrade, and install, i always get answers like this:

Err:4 bionic-updates InRelease
  Connection failed [IP: 80]

also in the end:

W: Failed to fetch  Connection failed [IP: 80]
W: Some index files failed to download. They have been ignored, or old ones used instead

Can anyone please provide solution? My internet works fine when browsing. I also use snap to install discord and it work fine. Thanks.