Perhaps Twitter account's blocked by right awful cad (8)
I believe the answer is:
birdcall
'perhaps twitter' is the definition.
(twitter can mean a bird's call)
'account's blocked by right awful cad' is the wordplay.
'account' becomes 'bill' (synonyms).
'blocked by' means one lot of letters goes inside another (I've seen this in other clues).
'right' becomes 'r' (common abbreviation).
'awful' is an anagram indicator.
'cad' anagrammed gives 'dca'.
'r'+'dca'='rdca'
'bill' enclosing 'rdca' is 'BIRDCALL'.
(Other definitions for birdcall that I've seen before include "(Device to imitate) song of songster" , "Sound of tweeters" , "(Instrument copying) songster's song" .)