You might want to check the documentation for what Serial.available() returns. It returns the number of chars available to read, not a number so your line:
if(Serial.available()>19 && Serial.available()<70)
will only be true if the number of chars in the input buffer is more than 19 but less than 70.
When you use Serial.print(), it takes a number and converts it into a string representation of that number and sends it over the wire. For example, if send = 12, the what gets sent over the wire is the string "12" which is two bytes (0x31, 0x32) so reading that in, you will never get the number 12 unless you convert it back Serial.parseint();