i have a column named datecolumn varchar (5). it contains data something like this:

datecolumn
26NOV
09DEC
18NOV
22DEC

now i want to make that data as this format :
26/11/
09/12/
18/11/
22/12/

i am trying to do in this way---
select substring(datecolumn,1,2)+ '/'+replace(datecolumn,substring (datecolumn,3,3),month(datecolumn))+'/' from temp_table

i am getting this error--
Syntax error converting datetime from character string.