Duplicate Count (Codewars)

def duplicate_count(text, checkTimes):              # RETURNED TYPE = DICTIONARY

    # 1. Find the different letters in the given text (ALL LETTERS WILL BE CONTROLLED LIKE BEING LOWERCASE)
    differentLetters = []
    for ch in text:
        if ch.lower() not in differentLetters:
            differentLetters.append(ch.lower())

    # print("Different letters: " + str(differentLetters))

    # 2. Create a dictionary: Every of the different letters ---> will go to 0 (0 is the initial frequency of appearance)
    # Dictionary will finally have: EACH DIFFERENT LETTER PAIREDWITH HIS FREQUENCY OF APPEARING
    dictionary = {}
    for letter in differentLetters:
        dictionary[letter] = 0
    # print("    Dictionary:    " + str(dictionary))

    # 3. I will scan my text to increase the values of the map
    # For every character "ch" in my string = text, I want to repeat the following process
    for ch in text:
        for i in range(0, len(differentLetters)):
            if ch.lower() == differentLetters[i]:            # That means I have a hit = (my character ch is equal to the i-th letter of my list differnetLetters)
                # Because of having a hit, letter "ch" is sure in my dictionary. I will increase by 1 its value
                dictionary[ch.lower()] = dictionary.get(ch.lower()) + 1
                break

    counter = 0
    for key, value in dictionary.items():
        if value == checkTimes:
            counter += 1
    return counter