Account paid

I have been trying for months now to get Vericred to understand that the account from 2012 that they are harassing me on was paid up at the end of 2012, beginning of 2013. <br> <br> This is so long ago that I am not even with the same bank any more and can't get the proof of payment. <br> On top of that the debt (which does not exist) has lapsed. <br> <br> The last conversation was that the account would be closed, now I get a final demand letter. <br> <br> What must I do to make you understand that I am not paying for something twice!<br> <br> Enough now.