Perhaps the condo is receiving the monthly payments later than you think they are. One suggestion might be to try sending your payment certified, return receipted so that you get a signature and know exactly when the payment is actually received by the office. If necessary, you might have to send the mail out earlier to assure delivery on time.
Other than calling and emailing - have you tried to FAX a letter to management? This also might generate a response from the company.
Unfortunately, this situation does need to be addressed directly with the management company.
Arlynn B. Palmer, ESQ, SRES, CBR, CMS, CNS
Assoc. Broker, REALTOR
Coldwell Banker Claire Sobel
(516)621-6300 x 205