Frederick County is helping 28 households work with a state commission to investigate claims that those using housing vouchers were charged more than other tenants in the same complex. The county’s Human Relations Department is working with the 28 households to file complaints with the Maryland Commission on Civil Rights, the county said in a press release Friday. The county Human Relations Department did an initial investigation in the case, but the state’s process requires that individual tenants file complaints with the state commission, county spokeswoman Vivian Laxton said in an interview Friday.