My wife is a Denver Public Schools teacher. She's been teaching for 3 yrs. This year in September when the school was adjusting the pay due to a new contract she thought her increase was too low. She called the accounting office to inquire. They investigated and told her that they had misplaced her on the matrix (of yrs of experience and education) when they had first hired her and they owed her back pay. The accountant needed to talk to her supervisor but would be back in touch. She called back and said the supervisor concurred, my wife was owed $9k and she would get a check. She did in October.
However, today she got a call from the accounting office. They said they made a mistake, give back $8700.

What do people think about this situation? She's already paid taxes on the $ and I'm a little reluctant to just give back a substantial amount of money in this kind of circumstance without giving it some serious thought. Has anyone had a similar experience. How did you deal with it? Any other advice? She has a union and has contacted her rep, but any other steps people think she should take?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13