I have setup maven proxy settings in conf/settings.xml as
true
http
If you are behind NTLM proxy, refer this solution that worked for me!
If you are using some IDE Like IntelliJ etc... please make sure you are changing settings.xml of the same maven which IDE uses! I mean there may be bundled Maven and if you change your system maven settings.xml it is obvious it won't work!So check IDE configurations.Please specify IDE name if you want more help on it.
Yes this one is silly but though worth to check out! check your system path environment variable for maven path which is exactly same of which settings.xml you are updating of.
hope this helps!