I am ready to pay in the lieu of notice but company not accepting

My offer letter statement: Probation: You will be on probation for a period of six months from the date of joining. At the end of the probation period subject to your satisfactory performance your services will be confirmed, and you will receive a letter to this effect. Notice for separation/termination: During probation, either party may terminate your employment with 15 days’ notice in writing or payment of 15 days salary in lieu of notice. Upon confirmation of your services, either party may terminate your employment with 2 months (60 days) notice in writing or payment of 2 months (60 days) salary in lieu of notice. The Company reserves the right to recover an amount equivalent to notice pay on a pro-rata basis if you fail to give to the company adequate notice of your intention to terminate your employment. Salary for this clause would constitute of your fixed Basic +DA and HRA drawn at that time. ------------------------------ I resigned on 6 months 20 days and not received confirmation letter. Now company forcing me to serve notice period as I am ready to pay in the lieu of notice. Already served 13 days of notice.