Deposits on the map

I own 3 of these card holders in over a year and can therefore be a long-term review. The shells look chic, but have a huge disadvantage. Because it occur on all cards that I have pushed the passage of time in the case, after a few weeks black deposits that look like dead bugs. Deposits that I can no longer be removed by repeatedly "polishing" over time. In addition, the magnetic stripe through the deposits is affected. Third, the card chip runs on black, which makes me sweat every time you use the card, whether it is time to read. I have been informed of this problem the company BMK 100 days after the purchase of the cases. They advised me to clean the covers. But how? I underline since repeatedly made with a narrow Q-Tip. Useless. On the contrary, the sheath characterized breaks at the edge. Whether you are therefore now in my purse, which I wear constantly in the back pocket, bend, I do not know. I note only that the shells now have a visible bulge, even when the card is inserted. I have now a very long time trying to look for the good looks and the high cost over the pesky problems away. After my latest map change by the bank but I will use the case from now on no account more.