hard question to answer. first of all your plan is very old. it does not exist any longer. i do not remember the exact specifications. but i think your original plan was 2mbps unlimited without any FUP for Rs. 3000.
long time ago, airtel applied a FUP of 100GB on all their plans. some users got it on their unlimited plans. others did not i assume.
and a while ago, all the pure unlimited plans disappeared. there are no plans with high speeds with no FUP. from what i see, you should be getting around 220KBps all the time. at least up to 100GB of data transfer. and then it should fall down to 120KBps for the rest of the month.
you say, you get a maximum of 60KBps. that can only mean one thing, you plan has been changed in the backend to one of the newer stupid plans and you have a terrible FUP. even at 256kbps i believe you should still get a minimum of 32KBps all the time in the month.
call them up ask them what plan you have and what FUP is applicable on it.
---------- Post added at 02:10 AM ---------- Previous post was at 02:09 AM ----------
since you have only mentioned about the upload speeds...
2mbps plan should have a minimum upload speed of 120KBps. and even after FUP is applied, it should be more than 32KBps.