Unsolvable Cipher?

If a message is encrypted with more than one encryption method, is it technically solvable? For example, if I encode a message using Vigenere ciphering and then I re-encoded this output using a poly-symbolic, non-letter alphabet would it be possible to decrypt? Without character frequencies (lost with the Vigenere) and pattern recognition (hidden by the poly-symbolic alphabet) I can't see how it could be done.