I would phone the Accu-chek helpline and tell them about your problems/concerns. They will probably ask you to return the meter to them, so that they can test it. They will send you a letter explaining what they found. This will hopefully prevent anyone else from having the same problem. The Careline telephone number is: 0800 701 000.
While you are on the phone with Accu-chek, ask them to send you some control solution. If you doubt your test results you can do a test with the control solution and if the results fall within the limits on the control solution bottle, your meter is performing correctly. You should check with control solution at least once a month, so that you are sure your meter is working correctly.