Cant use port

[the evil corperation]

I'm trying to port forward for a dedicated server using the port 28000, but it says the port is taken and doesn't work. I don't know to much about technology, can someone tell me what can I do to fix this problem?

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[the evil corperation]

EDIT: I found the thing using that port, its in UPnP mapping. Can someone tell me how to fix this?

[the evil corperation]

Problem fixed, locking