How to select a specific .m function when two exist?

Question

First, here the way i'm calling the function :

eval([functionName '(''stringArg'')']); % functionName = 'someStringForTheFunctionName'

Now, I have two functionName functions in my path, one that take the stringArg and another one that takes something else. I'm getting some errors because right now the first one it finds is the function that doesn't take the stringArg. Considering the way i'm calling the functionName function, how is it possible to call the correct function?

Edit:

I tried the function which :

which -all someStringForTheFunctionName

The result :

C:\........\x\someStringForTheFunctionName
C:\........\y\someStringForTheFunctionName % Shadowed

The shadowed function is the one i want to call.