Government Money Wrongly Sent To An Individual Account. Advise?

On Sunday, last two weeks my mom got a bank alert notification, someone sent her 3 million naira, she wasn't expecting money from anyone.

She was shocked, she called I and my younger sister. We couldn't believe it, so we waited for three days to see if the bank will reverse the money, they didn't, so I and my sister took our mom's ATM card to withdraw and test if the money was genuine.

We bought three phones from it. That's when we believed it was real. Then I transferred #50,000 to my bank and transferred #50k into my mom's other account which we used for foodstuffs.

On the fifth day the bank froze the remaining balance of the huge money sent. But no bank official or staff called my mom. That week passed, on the 3rd day of the second week, one lady called my mom by phone in the afternoon, she said her name is Sarah from so so bank.

My mom is not literate so they spoken in pidgin, she told my mom that she knows that my mom received a #3mil last two weeks and she has spent out of it. That the money was government money. Sarah told my mom to go to any nearest ........bank and write a mandate letter authorizing the bank to unfreeze the remaining #2mil in her acct and the bank will give us the beneficiary account which she will send the money back to. And we should return the money we spent out of it immediately.

When we got to my mom's bank, we went to customer agent area, instead of writing the mandate letter, we told the agent everything that happened leaving nothing untouched. the agent said we should give him the number of the staff that called us, when he called the Sarah with his phone, Sarah gave him another name, instead of introducing herself as Sarah, she said her name is Evelyn. She now told the agent to hold my mom down till she (Evelyn) gets to that bank to arrest my mom or whatever.

The agent said on what basis would he hold my mom down. The agent checked the description when the money was sent and he couldn't understand the description. He was saying how could this be government money. He told my mom to try and return the money spent and he told us to go.

The description on the transfer when it came in on Sunday was: "National Procurement of Scanners" #3million.

Is this truly a government money?