Airtel - Recharge benefit not received and I lost my Rs 251 without any use

Sir/Madam
As per the information provided by Airtel team on **-**-****,I recharged Rs.*** to my Airtel sim.But it didn't get activated mentioning that this pack is valid only on the sim which have already a unlimited/smart pack exist.But they didn't give me any information like this when I called them.So the next day (**-july) I called to cutomer care by pointing that it is their mistake and it is their duty to provide a detailed information about the pack we ask about..But he didn't give me any information..And after verifying my recording of yesterday's(*-july)they agreed that its their fault..But haven't taken any solution..After continuous calling to customer,On *th july they refunded me Rs.*** saying that Rs.** is gone as per GST..so,it won't be refunded.But by that Rs.*** which is refunded cannot be used for calling or internet..It means my full amount is wasted only because of their mistake..And because of all these issues I'm not able to attend my online class for * week..I want justice sir..
When I call them again to ask what can I do with this refunded Rs.*** they say sorryy you cannot do anything and they cannot provide any other solution..I'm totally down air..I recharged it to attend my class but I'm not able to..Please do take it very seriously and get me a solution for it.