Write properly a formula in Excel VBA

I already asked a question like this before, but seems that the answer given is not working in this case

this is my code:

Worksheets("Sheet").Range(myRange).formula = "=CONCATENATE(CODICI!"& stringCodiceCella & ";"& stringDesignazioneCella & ")"

Note that stringCodiceCella is a String, and stringDesignazioneCella is also a String.

Following this link A working example of formula in VBA

I can't see the error.