Hello Nabeen,

To make sure 8870 is working, remove your MCU and apply dtmf to decoder. Check the output from decoder and dtmf present pin(StD, pin 17 of your 8870). The StD pin should go high when a dtmf signal is detected. If you get proper output from decoder, then you check your micro like port initilisation, checking StD pin etc etc.

regards
Murugan AKT