Re-dial correctly, or get off the line (6)
I believe the answer is:
derail
'get off the line' is the definition.
(I've seen this before)
're-dial correctly' is the wordplay.
'correctly' is an anagram indicator.
're'+'dial'='redial'
'redial' with letters rearranged gives 'DERAIL'.
'or' acts as a link.
(Other definitions for derail that I've seen before include "stop things going smoothly" , "go off line" , "Cause to run off the tracks" , "Cause to leave the tracks" , "Cause to come off the tracks" .)