Clueless with Account payments

Been at NHC Bryanston on the 17-08-2015. Paid the drs fees of R520 straight after I've seen him and received statement'. One day after received an SMS stating that I owe NHC Bryanston R520, and will be handed over if payment is not made asap. Reallyyyy ???? Contacted them today to find out what the issue is with the SMS after i''ve spoken to 3 people at reception who could not told me what it's about, then when I asked to speak to manager ... this is how he answered the call from a client ... \whats up". How unprofessional ... This is the last time I will visit NHC"