First Plus - Elderbridge Ltd end of fixed term issues

[Robsthename]

Hello, we took out a secured loan 2006 with First Plus over 180 months. We were expecting to finish the loan next year 2021. We contacted Elderbridge as they had taken over the accounts of First Plus to confirm this as the total amount paid to date was the amount we were expecting to pay in total as outlined at the start of loan. We were told on the phone that we had a zero balance to pay and the loan was paid off. A week later we received a letter from Elderbridge stating that it was a mistake and we now owed a sum of money that had no relevance to the state of the account at all. We lodged a formal complaint with them and then received a letter stating that some interest had been not applied to the loan and now they were applying it. They said they did not need to declare this under the current law. *As you can imagine we are devastated and very confused as to be told this. Any advice would be appreciated. Many thanks *