Usage of that and those

Which is the current usage of that and those in the below-mentioned scenario?

Bar(s) that have been purchased by the customer.

How can this be the right sentence when that generally is used to refer singular objects?

Or

Bar(s) those have been purchased by the customer.

"That" as referent applies to both singular as well as plural items. "Those" is exempted from such cases. For this reason, "Bars those have... " is incorrect.

The distinction arises when they are used as demonstrative pronouns and demonstrative adjectives.

Thus, That is my pen; Those are my pens.

and

That apple looks juicy; Those apples look juicy.