I received a loan on my house from the bank, a week later they say there was a mistake and have put a hold on my account

I received a loan on my house for home improvements. Paperwork was signed, money was deposited. The paperwork clearly states the amount deposited. A week later the bank has put a hold on my account, so that they can reaquire some funds. They are stating that they gave me more than they should have. and need about 3500 returned. According to the paperwork signed by the bank, and myself, I received exactly what I signed for. My question is, how am I liable for this? Or who is Because I am only going by my paperwork.