Student loan payments refund timeframe?

Hi, I received a letter stating that I was owed a sum of money, as I had been paying for a student loan without being a borrower. I sent off the form over three weeks ago which requested my bank details but I still have not got the refund. Any idea how long the refund takes?

Hi,
You can find out whent to expect a reply here:
Check when you can expect a reply from HMRC 
Thank you.