Given a summons to court for eviction, because of non payment, but we have proof of payment?

My parents received a summons from the court stating that they are being evicted because of non-payment. However, my parents have the cleared check copies from the bank where it clearly shows that the landlord cashed all of the checks… What can we do? The landlord has hired an attorney should we do the same? Or are my parents okay since they have proof of payment? Thanks in advance!