Theft via account non-closure

I closed my TFG account on the phone and paid all costs in January this year when at the end of the month I received another bill I went in store and closed it again. TFG promise it was closed. I then received another months invoice. Now they can’t close it on the phone and with lockdown the store is not open. They have obstructed the closer of the account for their own financial gain and continue to ignore emails and calls remain on hold.