Decryption not working if key has same symbol like text

[Paragoon2]

I'm trying to decipher the text from ADFGV cipher where is matrix, alphabet and key, but I don't know how to fix it if the key has the same characters.

 def decrypt_ADFGVX(self, cod, key):
    """ Decrypt with the ADFGVX cipher. Does not depend on spacing of encoded text """
    matrices = list('ADFGVX')
    chars = [c for c in cod if c in matrices]
    key = list(key.upper())
    sortedkey = sorted(key)
    order = [key.index(ch) for ch in sortedkey]
    originalorder = [sortedkey.index(ch) for ch in key]
    base, extra = divmod(len(chars), len(key))
    strides = [base + (1 if extra > i else 0) for i in order]
    starts = list(accumulate(strides[:-1], lambda x, y: x + y))
    starts = [0] + starts
    ends = [starts[i] + strides[i] for i in range(len(key))]
    cols = [chars[starts[i]:ends[i]] for i in originalorder]
    pairs = []
    for i in range((len(chars) - 1) // len(key) + 1):
        for j in range(len(key)):
            if i * len(key) + j < len(chars):
                pairs.append(cols[j][i])

    decode = dict((v, k) for (k, v) in self.create_encode_dict().items())
    return ''.join([decode[pairs[i] + pairs[i + 1]] for i in range(0, len(pairs), 2)])