Issue with moving out


I have moved out of my flat about 2 months ago, and submitted my readings for the last day in the property. Bulb has wrongly recorded them as provided a month earlier, and charged me an additional “estimated” month of usage. I have had a number of conversations with them, where they said it will be fixed, but nothing is happening. They have ignored my last 2 emails. Anyone had that issue, and managed to deal with it?