6500 Touch Screen Problem

[pckopat]

I have got some 6500 touch screen phones. I was change this phone imei with spiderman box. But when that phones have using some days later reset the imei it self be automatic and turning factory imei. For example i will change this : 356************ later it be so automatically : 135***************
And not one , two all phones giving this problem. Please support me how can i fix this big problem??