Bill was in debt and it surged (8)
I believe the answer is:
billowed
'surged' is the definition.
('billow' can be a synonym of 'surge')
'bill was in debt' is the wordplay.
'was in debt' becomes 'owed' ('they owed' means 'they were in debt').
'bill'+'owed'='BILLOWED'
'and it' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for billowed that I've seen before include "Swollen account was due payment" , "Flowed with an undulating motion; filled with air" , "was swelling" .)