My transaction is still in mempool for 3 months now ...
Why is it not getting out of the mempool?
It's been 4 months actually, but this is because you used minimal fee 1.00 sat/vB so transaction can't be confirmed and I honestly don't remember last time we saw fees getting that low.
Don't expect it to see fees go down that level any time soon, so better do what LoyceV suggested above.