Overpaid by employer

I am humbly asking for any legal thoughts on what I am going through right now. I was recently informed by my employer that they overpaid me for 1year. They want me to pay them back what i owe at my own pace and time by salary deduction which i am very much willing to do. Fair enough but not until I realized that when I had my 6th month appraisal, they didnt let me sign my Personnel Change Notice (proof of appraisal) which is for my strict compliance. They always had alibis. It is obvious that back then they already knew about this but they let it pass. Its only now theyre raising this issue since this may affect their audit. Even though I have benefited from this I feel sort of oppressed cause they prolonged it and now i cant make future plans because if I base it from the amount they want to deduct from my salary it will take years before i can fully pay it back.I also feel that there was negligence on their part as I would think they wanted to cover it up. If this was resolved earlier less hassle/damage for me. Will I have reasonable grounds to put up a lawfully fight?

overpayment usually happens when employers try to cheat out of taxation. were you taxed at 2%? 15% or the regular 30-32%?

i recommend you work out a fixed payment schedule. unfortunately, the company is entitled to get back the money. make a written follow up regarding the appraisal so you have a record.

Thank you sirs. Im enlightened.