Worst Service at Nokia Care Service Centre

Respected Sir,
Within 1 month of purchase of my handset Nokia 220, I realised that the ringtone volume decreases suddenly without any notification. Whenever any call comes in my phone, I cannot hear it ringing. For this problem I took the phone to Nokia Care Service Centre. But after 1 day of invigilation, they told me to keep on increasing the volume of handset’s ringtone when I realize that it has decreases. They cannot give any other solution and they are also not aware of the problem. They donot know what to do and got puzzled. This is not the ultimate solution of the problem, I think.
Please look into the problem and do whatever required.