If you really want to get legal on their arses, tell them in any response that you're exercising a right of set-off under rule 14.25 of the Insolvency Rules 2016, and setting off against any debt the unliquidated damages owed to you arising from their breach of contract under an implied term to take reasonable skill and care, noting that under rule 14.25(6) the term 'obligation' means 'an obligation however arising, whether by virtue of an agreement, rule of law or otherwise'.
If you really want to get legal on their arses, tell them in any response that you're exercising a right of set-off under rule 14.25 of the Insolvency Rules 2016, and setting off against any debt the unliquidated damages owed to you arising from their breach of contract under an implied term to take reasonable skill and care, noting that under rule 14.25(6) the term 'obligation' means 'an obligation however arising, whether by virtue of an agreement, rule of law or otherwise'.