Severence rehired and fired

i worked for ABC Sliced Bread in S.F. Ca. I am a member of Teamsters Union. About 5 weeks ago the plant i worked in closed. On the last day we were given all the pay we had coming except the severence pay, they said it would be mailed. A week after closing i was called to work at French Bread in Oakland, Ca. When my severence check arrived I cashed it. Then about a week later I was told to give back the severence check since i was given another job. Both companys are owned by ABC. When i told them i cashed the check i was excorted off the property where i was working and told i had 3 days to repay the severence amount I received or my employment is terminated. i offered to pay it back in payments since i did not have the full amount but was refused. Is this wrongful termination and was i entitled to the severence(it is in the union contract). I was unemployed for a week but the company says it was a transfer. Many of us at Sliced Bread applied for French Bread before the closure of Sliced Bread. I received a letter thanking me for my application but all positions had been filled.