USB stick for internet connection

Location/place: bangalore

Name of company/service: vodafone south limited

i purchased an USB stick and SIM 9866657042 on 25th march 2011 from sheshadripuram vodafone store.the internet connection worked for a 3 months.later,the inernet connection was very difficult.i contacted vodafone call center.their technitians visited my residence,/5 times. since,it did not help i requested them to cancel my connection and refund the cost of the USB stick rs.1500 plus deposit amount of
300rs.on 11th jan 2012,GM customer service has sent a cheque dated 6th jan 2012 for rs.641.i have not encashed the cheque.earlier, when i talked to the manager,sheshadripuram store,asked me to keep the USB stick till she called me up.that day has never come.i request you to arrange for the refund of 1800/= at the earliest.