Stone fell out

i took my ring in for rhodium plaiting , 5 days after collection my centre stone which is tanzanite fell out. i took it back in for repairs . take note th ering was puchased for R3200 i was told that i would need to pay R2780 to get it fixed. this is day light ******* , the other stones are there , so is the metal why should i be charged so much to fix a ring . its short of buying another one , this is so unfair not only had i taken it for cleaning a few days before am assuming they could have at least told me that the claws on the ring are worn out. So this goes to say that their ring are not of good quality cause i totally do not understand why i need to pay so much . i have sent them mail and called a lot of times to no avail .