You make a note for your diary for 20 June to contact the court if you haven’t already been notified to see if the claimant has paid the court fee.
Is there more, ie deadline for submitting papers to the court? It’s important to know when you need to submit your witness statement by. It could be that this date is after the date for payment of the court fee, so you need to think about what you’ll say now but don’t worry about writing this down until you know the fee has been paid.