In logic, two negatives cancel each other. So can’t hardly would mathematically mean can easily – which is the opposite of what you intend.
because the word "hardly" already functions as a negative (meaning "barely" or "almost not"). Quick Comparison is it can hardly or cant hardly free
Using is not standard, though you might hear it in some dialects or casual speech. For proper writing and clarity, avoid "can't hardly." In logic, two negatives cancel each other