Check you incoming tds, the tds after RO and before DI
The RO should remove about 95% of dissolved solids. If it's still 019 after DI then either your DI is too small and is depleting very quickly or there's something wrong with you RO - maybe the membrane isn't seated properly and waste water is finding its way past the membrane and into your DI.
My 40-40 reduces tds from 300 to 022 (not brilliant, but I can live with it) and my 6lt DI brings that down to 001 and the resin lasts about 3-4 weeks.