SIM900 - HTTP / extreme data ratio

Hello,
i tested transmit data to serve by HTTP. I tested for a four hours maybe and only sometimes i posted request. But data traffic from my SIM card for this time is 300 MB!

I sent only body with content "XXXXXXX,dd.dddddd,X,d.ddddddd" and response is "Xdd,d.dX". I know about header data weight, but also this is extreme data traffic for this small data.

Is problem with SAPR or initHTTP? I call commands (down) in loop every 30-60s. I

//simply code without delay and reading buffer
                GPRS_COM.println("AT+CGATT?");
		GPRS_COM.println("AT+SAPBR=3,1,\"CONTYPE\",\"GPRS\"");
		GPRS_COM.println("AT+SAPBR=3,1,\"APN\",\"internet.t-mobile.cz\"");
		GPRS_COM.println("AT+SAPBR=1,1");
		GPRS_COM.println("AT+HTTPINIT");
		GPRS_COM.println("AT+HTTPPARA=\"URL\",\""+String(DEVICE_API)+"/IncomingHandler.ashx?Data=" + data + "\"");
		GPRS_COM.println("AT+HTTPACTION=0");
		GPRS_COM.println("AT+HTTPREAD");
		GPRS_COM.println("AT+HTTPTERM");
		GPRS_COM.println("AT+SAPBR=0,1");

Thanks for help. I use this module Arduino GPRS Shield - Geeetech Wiki

You need to check to see if only one data byte is being sent in each data packet. This might be happening using the “print” function.

Do you know, how can i check this on GSM? And exist another method for send commands to the module?