If you have been informed that the pension amount has been regularised which is actually nothing but a reduced amount and you have been quoted the reason as well as the provisions of law for modifying the pension amount, you may first ascertain the facts 

The OM what you referred may be of use to you to quote the relevant law in this regard in order to get relief. 

You can first make a strong representation to the competent authority, i.e., your employer and request to cancel the orders passed by it which actually reduced the quantum of your pension.

If you do not get any proper response or your request is rejected, you may file a writ petition against the employer citing the supreme court judgment in this regard and knock the doors of the court to get justice. 

Your understanding is correct 

organisation cannot seek to reduce your pension 

file writ petition in HC against reduction of your pension 

Recovery has been made effective from your pension after almost three months short of 5 years. The action of your employer contravenes the OM dated 02.03.2016 issued by DoP&T. The Hon'ble Supreme Court has discussed and held that such recoveries are iniquitous and therefore arbitrary. You have rightly pointed out wherein, recovery from retired employees is impermissible in law.

You may write to them (your employer) to stop such recovery immediately citing this OM. In case of not getting any relief from your department, you may approach CAT by filing OA.

Yes it's correct

Dear Client,

you can issue a legal notice to them to provide the correct amount of pension. 

- As per Pension Rules , Pension are not in the nature of reward but there is a binding obligation on Government which can be claimed as a right.

- Further, it can be forfeited only on resignation, removal or dismissal from service.

- Further, a pension is sanctioned, its continuance depends on future good conduct vide Article 351, CSR [Rule 8, CCS (Pension) Rules, 1972] but it cannot be stopped or reduced for other reasons.

- Hence, your pension cannot be reduced for the said reasons of incorrection of scales, 

- You can give a compliant to the competent authority against the said employer.