Walmart Payroll Reversal

So, I got fired while off the clock and was planning to return the work phone when I went grocery shopping after I received my final paycheck, but they have reversed the bank payment. I'm thinking this is because of the phone I'm looking for help to confirm if my theory is correct. On another note, in Massachusetts they're supposed to send the paycheck immediately upon termination, which they didn't. They waited until the next payday.