The machine I get RO from tested at 12 ppm TDS and all of the brewing ions were <1 ppm from a ward lab test.
Tell them their RO is not as advertised. Find a new store to buy RO from.
Here is my RO water from a store machine, then my tap water.
There are 2 reports here. Store bought RO water, and then my towns water. Samples were last December-ish.
I use the RO for brewing and add different salts to get the profile I want.
RO Water, Milford Michigan tap Water
pH 6.3, 7.8
TDS 12, 630
Cond. mmho/cm 0.02, 1.05
Cations/anions me/L <.1/<.1, 11,10.8
Na <1, 58
K <1, 3
Ca <1, 114
Mg <1, 33
Harness CaCO3 <1, 423
Nitrate <0.1 (Safe), 0.3 (Safe)
SO4 <1, 16
Cl <1, 132
CO3 <1, <1
HCO3 <1, 364
Total Alkalinity CaCO3 <1, 298