Final estimated meter reading is way off and Bulb not responding

We moved home a while back and closed the account. The property which Bulb was supplying the energy for was unoccupied for the last month hence our final meter read we provided was not different from the read before as the gas was not being used. I guess Bulb did not like that much and rejected our meter read and instead used their ‘estimate’ which was way higher. I do not feel ok about paying for gas that we did not use. Does anyone have a similar experience with Bulb and if you have managed to get them to fix it? They have being ignoring my emails completely and it is literally impossible to call them. The last time I tried I spent 30 mins on the phone and no human being answered the call.