Airtel — receiving due massage after having ported my mob number from airtel to bsnl

I have got ported my mobile no. [protected] from airtel to bsnl.

Before accepting port request, i had paid all previous bills to airtel even additional payment till port request is accepted. The detail is as under-

Bill plan during airtel service - rs. 99/month

Bill generation date by airtel[protected]

Last bill paid rs. 150/- agaist bill amount rs. 131.71/- (Excess paid rs. 19.29/-) on[protected]. E receipt no. [protected]

Rs. 50/- was additional paid for using airtel service till acceptance of port request. E receipt no. [protected]

Port request is accepted on –[protected]

Bsnl service start from –[protected]

My due amount was in minus rs. -69.29/-

Even then i received massage from airtel about due amount rs. 586.01/- while it was already in minus. How would it be possible that much due amount at having plan of rs. 99/- per month from 13-03-18 to 27-03-18 and it was already in minus.

Kindly inquire into the matter and provide justice and get it waived off.