you can check whether a record exists or not before inserting it.
you have two options at this point.
1- you may ban an insertion completely if there exists another record having the same fields.
2- you may put a time-limit for it if actually such duplicated data may exist. this option requires additional 'DateTime insertDate' column on your table.
for the first option,
if not exists select 1 from TableA where ColA=@a and ColB=@b
insert into TableA(ColA, ColB) values(@a,@b)
for the second option
if not exists select 1 from TableA where ColA=@a and ColB=@b and DATEDIFF(mi,insertDate, GETDATE())<5
insert into TableA(ColA, ColB, insertDate) values(@a,@b,GETDATE())