Welcome to the Community.
Just to confirm things ....
Are you working with a "report" or something that is used as a "database"?
If a report I assume you have created a template, trapped the fields you need and the result is a populated table that you now need to filter some more.
Just to see what is going on a little more clearly try creating one filter for "C" and another for "V" and checking that both give the result you expect.
You can then create a compound filter to see what happens what you use them together.
As written your formula is not as it needs to be.
You could write it as:
LEFT([Field],1)="c" .or. Left([Field],1)="v"
Or simply define each filter separately as previously suggested (they may also be useful like that?) and then create a compound filter that includes both of them, getting 3 filters for the price of 2!
(I should point out the these are no the only options here but they are the ones that seem to make some sense for your immediate needs.)