Different AFSK mark and space frequency

Hi, I found a "strange" AFSK signal in my area. It is AFSK, I think, but mark and space are 900 Hz and 1500 Hz (not 1200 Hz and 2200 Hz like a standard, Bell 202, AFSK). Do you have any ideas how to decode it simply? All the programs I found seems to work only with 1200 Hz and 2200 Hz standard.