very low speeds than told

Location/place: calicut/kerala

Name of company/service: idea/3g

i recharged my phone with rupees 949 for idea 3g according to an information given by a customer care executive who told me that i would get speeds of 21.1 mbps(depends on phone) after the recharge until 6gb after which speed decreases to 3.6 mbps
.for a few days i started recieving speeds of 1.5 mbps though my phone supports 3.6 mbps after 1 week my speed became very low and reached to about 0.02 mbps.when i complained they told me the problem was of server complaint and would be resolved within 24 hrs.after this time when i got it connected my speed was only 0.06 mbps.when i contacted the customer care they are very busy .