Help needed

Gaz141265

So we had 2 endowments on our mortgage which matured before Xmas, thought we would need to pay both to the mortgage and then maybe a small top up. So first one was paid to the account and we were told the balance, which we thought was wrong ,the bank checked and said no that is correct so when the second one matured we went to clear the mortgage,the bank treble checked everything and it turned out we had £7500 to keep from the endowments and the mortgage was clear. Deeds for the house were sent to us by the bank all good or so we thought.

Extra money was used to mono block the drive and a new sofa etc, still some left but not much about £1500

Now 5 months later we get a call from the bank saying they made an mistake and we own them £14000!!!!!!
Not sure what to do,but really scared about what to do next, any help on this would be great!!!!