Airtel — charge after cancellation of connection fraud

Mater in 2019.
i had a landline connection by airtel which after great difficulty i managed to get hold of them on customer care and cancelled it as i was due to leave the country . i even recieved a cancellation confirmation call . i cancelled the connection on 20th april 2019 and yet im still recieving bills for it .
landline connection number :[protected]
amusing part is that i recieved a bill that is different than my actual plan. they reduced it to a base plan and are generating bills without usage every month.
im currently in the united arab emirates.