How do we handle benefits deductions we didn’t quite get right?

Q: "We merged our benefits with our parent company and the benefits deductions did not come out last payday. Can we double the benefits premiums on this paydate? Also, our benefits premiums are off by a few dollars from the parent company's premium rates. Do we need to charge them to what we told the employees at the beginning of the year, or can we use the new premium rates? We have employees in PA, SC, AL, FL, TX (where the majority are located), AZ, CO, MN, OR, CA, MO, IN.  - Vanh, Texas