Looking up a value based on two cells

I am having trouble getting anything to recognize the following situation, but it may be because of my own limitations.

I have a hidden reference sheet the displays the following (these are examples only, the actual list is much more confusing)

Products Plans Code
a 1 z1
a 2 z2
a 3 z3
b 1 z4
b 2 z5
b 3 z6
c 1 z7
c 2 z8
c 3 z9

There are a total of about 100 codes with product combinations and I would like to write a formula or code that looks up the products column and the plans column to return the code. I am tired of doing this manually!!!

On our submittal form there is a column that represents each of these columns and I want to select the first two from a list and it fill in the 3rd.

Any ideas on how to do this? I have been trying without success using lookup, index, match...Thanks!

Array formula (confirm with Cntl-Shift-Enter instead of Enter):

=INDEX(Hidden!C1:C100, MATCH(A1 & B1, Hidden!A1:A100 & Hidden!B1:B100, 0) )

Thanks, that took care of it!!!

I was missing the and in the second argument for the match statement.