sink bought in February 2019 (one of the cheapest ...

sink bought in February 2019 (one of the cheapest on the net) of very poor quality. mark very quickly, the traces do not leave even with white vinegar as they advised me.
At first it was because of the so-called limestone.
Limestone that in 4 months makes brown traces in the sink bottom never seen, plus there is a softener with 8 th output so ...
Fortunately I did not buy the kitchen there.