"Task is to find the all the debt_code (account number) which have been at least once in 133 repcode in the last one year and if they are still in the same repcode."
Any repcode that's currently in 133 also meets the requirement of have been at least once in 133.
If the requirement really is as you formulated it then you just need to check if the latest repcode for a specific debt_code is 133.
Your sample data is missing the date column - but let's assume there is a date column called dt then the SQL could look like:
proc sql;
create table accounts_in_133 as
select
debt_code
,max(dt) as latest_dt format=date9.
from p2scflow.debt
where rep_code='133'
group by
debt_code
having max(dt)=dt
;
quit;