Anyone use a ST109 tracker?

[Daffy D]

About two years ago  I installed a ST109 tracker on the family shopping bike.

 

The tracker works fine and gives location of the bike within a meter or so.

 

The problem is with the SIM card payment. Initially 50฿ would be enough for a month without topping up. Recently the topping up time has become shorter till now the SIM will only work for just 10 days before needing to be topped up again.

 

Anyone have the same model tracker experiencing the same? if so, did you find a way to fix the problem? and get back to the 50฿ per month.

Thanks.