MB deducted incorrectly

MB not wi fi. Every time load GB package, Vodacom ignore 1 they were deducting from now new 1. Complained last month agreed I'm right. Again they were deducting from 1gb and 850 left expires on 13/12. Received new 1gb on 01/12 immediately started deducting from new 1. Complained, 1st never got back. Again yesterday same, today refuse to rectify. SMS says last 1 comes 1st & 1st comes last, so 850mb expire on 13/12 new 1 on 31/12, refuse to finish 1st 1 so lose it. They deducting from new 1 &350 mb left still are. Number ********** 763 shows new 1 still. How can load MB have to wait til old ones finished, because you will lose it. Phone to complain 3x today takes you right through at end says unforseen circumstances call centre not available. Straight *******ion.