The system keep invoicing incorrect invoice

Customer has been paid $3500 on 26/4/2017, the lease renewed to 25/5/2017, and $200 unpaid.

But the system keep invoicing the customer $3500 since 4/6/2017, about 10 times, which the invoice is incorrect.

It freak the customer out. It happened twice on different customer, please help us to solve the problem.