Android Set doesnt delete checked then unchecked value in arraylist

I have an array list that contains all the checked items and a hashset to prevent duplications. But now I have a problem that the array list still stores the previously checked items even though i have unchecked it.

I have looked for solutions like Hashset and using (!isChecked) but those wont delete the previously stored value.

       viewHolder.checkBox.setTag(dataModel.getChkBool());


    viewHolder.checkBox.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
                    if (viewHolder.checkBox.isChecked()) {
                        citiesSelection.add("\n" + dataModel.getCity());
                    }

            //prevent duplicates
             hashSet.addAll(citiesSelection);
             citiesSelection.clear();
             citiesSelection.addAll(hashSet);

            Toast.makeText(getContext(), "Checked Total: " + citiesSelection, Toast.LENGTH_LONG).show();
        }

    });

Screenshots:

Checked boxes

Unchecked, but the arraylist still contains the previously checked ones