Unable to receive SMS on Android
In the SIM900 is an AT command that let you do a factory reset, your module will restart to the default values. It must be an AT command very similar to the SIM800.

The AT commando that (perhaps) will work for you is the ATZ, in the SIM900 works for me.

You can look over here to see what command is. Look over page 33. And be carefull, the link that I send to you is the AT command list for the SIM900, not the SIM800.

Hope you can find an answer.