How to contact Instagram about login issues???????

Hi everybody
hope this is the right place to ask about the issue I'm facing.
Thing is I'm "partially" locked out of my Instagram account; I'm saying partially because I can still make the access from my phone app but I can't access anymore Instagram from my pc as my username is not recognized, though is obviously the same I have in use on the mobile app.
It all started when I installed the usual browser on a new computer and wanted to get to Instagram from that machine; I got a message saying "the username doesn't belong to any existing account"
Very odd because when I try to reset the password, the username is correctly recognized and I got the reset link in my registered email account; but then once I create a new PW I soon after get an error message that says "the page you're looking for doesn't exist or link is corrupted"
How can I contact Instagram to sort out this problem???????
thanks