product defect

Ipuchased 1 enance uv on 08/03/2012 for Rs.11490 but from the date opurchase there was leakage problem the serviceman were after 3 to 4 phone calls, they come and will putting the tape and go but the the problemwas repeating till the 1 and half year then they told there is no gaurentee because the 1 year gaurentee period over and said to take service contract for 3010 rs , then i took the service contract on 26.07.13 and then they changed the part and it woked for 1 year and then the leaking problem started on 20.011.2014 but still now it as not rectified the serviceman will come does something tell us it has done but it is not rectified we then call them upto 3 or 5 times they come but it has not rectified and the problem is repeating so kindly do the needfull it is better to exchange the unit the service people tell that when you complaint we are attending then whats your problem but it is not 1 or 2 time problem but it is repeating from the purchase date to still now