Can you log on your bank account to 'see' which one it is?
My bank scans a copy of the cheque into their system so when it shows up in my account as 'NSF' I can click more info and the cheque shows up .... otherwise it can take 7-10 business days for the actual 'NSF cheque to get mailed out' and I would not be waiting that long to deal with this ~ I would call the bank if they do not have this service and see if they can find out WHO bounced!
Either way IF the client has not already come in with CASH for me cause IME they typically know BEFORE me that their cheque has bounced on their end but if not than I would contact them at work or home and tell them cash is needed TODAY including my NSF fee in order for care to continue ... if they did not than according to my contract their service is terminated and they forfeit their Security Deposit which would be use to cover any care already received and than time to find a new client!
I still prefer the 'paper trail' of cheques for income tax purposes and I am too cheap to pay the EMT and other electronic services charges at this point cause i have not had any issues with cheques .... however you only get one 'shit happens' excuse and if you bounce another cheque on me you become a 'cash only' client!