Airtel India - Recharged for 558 but they started 598 plan without my consent

My airtel number is **********
My case is really different from the rest of complains. I recharged for ***,for * days it worked fine . I got * gb data.
But after * days AIRTEL changed my plan to ₹*** which gives *.* data per day.
Now I tried complaining for a week to airtel who told me they will resolve it. But they denied it.
Their agent changed the plan without my consent. This *** plan is useless to me. Data is spent in half day.
Although, why should i get the plan I never asked for. They just mistakenly did this.
Kindly help me in this.
I need to get the plan I recharged for. I have all the proofs that I recharged for *** and used it for * days.
I need to get the *** plan back .