Don't give a win for personally dismissing you. You get yours brother!
If your monthly pension offer is 6% or more of the lump sum then it may be worth considering keeping. If it’s below 6%, then the NUMBERS suggest you likely do just as well (or better) by taking the lump sum and investing it. Paying yourself each year.
Take your monthly pension offer and multiply it by 12, then divide by the lump sum offer.
Example: $1,000 a month for life beginning at age 65 or $160,000 lump sum today? $1,000 x 12 = $12,000 divided by $160,000 equals = 7.5%.
Surly age to begin a monthly pension and projected longevity after than date are considerations too but, you start with that 6% rule. Don't leave any more of your money on the table for them than they have already demanded of you.
I know you just want to be done but, that is your money, not theirs granted you anymore. You earned it long ago. Don't unknowingly short yourself to cut all ties and benefit them further.