Modify GSM module code to receive SMS and do actions accordingly

Projects Programming
4

Hello again!

I've managed to somehow connect GSM with my Keypad without disabling functionality of the keypad, but now, everytime my loop which looks like this:

if (sms_position) 
       {
           // read new SMS
           Serial.print("SMS postion:");
           Serial.println(sms_position,DEC);
           sms.GetSMS(sms_position, phone_number, sms_text, 100);
           // now we have phone number string in phone_num
           Serial.println(phone_number);
           // and SMS text in sms_text
           Serial.println(sms_text);
       }   
       else
       {
           Serial.println("NO NEW SMS,WAITTING");
       }     
       delay(1000);

returns me -2 as a sms_position, so it keeps going and overloading the program and my keypad is working very slowly, and it does not receive any messages and I think that's the problem why. But why does it give -2, not -1 or something, how the hell does this even happen? Maybe some of you guys have encountered such problem before and could help me out? Thanks!

This is the GSM shield I use: https://www.ebay.com/itm/SIM900-Quad-band-GSM-GPRS-Shield-for-Arduino-UNO-MEGA-Leonardo/221176159800?epid=1555353015&hash=item337f205e38:g:ZgEAAOSw-29ZPqAk