And sending a flat denial is not accepting or acknowledging the debt. You are saying that there is no debt ! What acknowledging the debt would be saying that the debt exists and you wish to pay part of it. The importance of that is that there is a time limit for claiming a debt. If the debtor doesn't accept that there is a debt or doesn't reply, the time limit (6 years) expires and the creditor can't get the money. However, if he makes the mistake of agreeing, within the time limit that there is a debt, the 6 years starts all over again.
In your case, nobody is going to forget and if they are going to act, they must do so within the time limit, which they may well do because they think that you have gone quiet because you owe the money.