Wish Net — internet speed

My internet speed had been around 1.5 mbps while surfing youtube and more while downloading for past 3 months. Now it is back to 500 kbps. I have not changed the pack since i got the connection. Why is this happening. My service provider is not giving me satisfying reply. My id is suryasekhar_kb. Registered number is [protected]. If i don't get a reply from you i will think of changing the connection. Thank you.