Request for a "voorlopige teruggaaf" filed by mistake
You mention that you filed a request for a provisional assessment for 2012. This seems strange since a request for a provisional assessment can only be filed for the current year, so for 2013. A request for 2012 can‘t be filed since that year already ended. Instead the applicable tax return must be filed. The tax authorities should indeed ignore the request.
The M form must be filed on paper and can‘t be filed electronically.
The tax authorities will have received something they can process since they have sent you a request to provide your bank account number. You will have to provide the account number any way to receive the refund based on the M form which was filed for you.
If you did file a request for a provisional assessment you can cancel it again by filing another request showing a nil result. But you can wait with this till you receive a tax assessment from the tax authorities. You can also file a letter of objection once you received the tax assessment.
Check the correspondence which you receive(d) from the tax authorities thoroughly.