Hard to contact us? Ring in (7)
I believe the answer is:
callous
'hard' is the definition.
(similar in meaning)
'contact us? ring in' is the wordplay.
'contact' becomes 'call'.
'ring' becomes 'o' (letter resembling a ring).
'in' is an insertion indicator.
'call'+'us'='callus'
'callus' enclosing 'o' is 'CALLOUS'.
'to' is the link.
(Other definitions for callous that I've seen before include "Hard and unfeeling" , "Cruel and unfeeling" , "Not feeling" , "Cruelly unfeeling" , "Insensitive, cruel" .)