Thanks for your question
That's odd, as you have either been on BR since Jan 2012. or your employer has received notification to change your tax code to BR. Either way, you will need to ring HMRC on 0300 200 3300 as this is the quickest solution and although the opening times are8.00 am to 8.00 pm, Monday to Friday
8.00 am to 4.00 pm Saturday
I would suggest you try ringing as soon after 8am as possible, and as near to closing time, with a more successful chance of getting through to an officer (and quickly!)
If you have been issued a P2 notice of coding detailing this change of code to BR, then this would have contained an explanation as to why your tax code had changed, but somewhere along the line, HMRC think this is not your main employment, and there could be a number of reasons for this mistake but the key is get it put right as soon as possible.
If you have been on code BR since Jan 2012 (which I doubt that as that's over a year ago) then earlier tax year refunds will be due.
But ring HMRC as soon as possible as this is clearly wrong, and you do not want to suffer any longer than necessary!
If you have any follow up questions, please do ask, but if in the meantime you could rate the level of service I have provided, it would be appreciated, as this ensures Just Answer pay me.