Bajaj Auto — during free service charged oil ring replacement charge

During my 3rd free service. Ndm bajaj service charged oil replacement ring charge. Rs 66.00. Where as during free service. Part replacement charge is not charged. During 3rd service oil of engine is replaced and with oil and filter and o ring is replaced. Filter replacement is not charged. But o ring replacement is charged rs. 66.00. Please do the needful.