W.S. I cannot say about conventional banks, but Islamic banks never give a fixed payment plan for 20 or 25, etc. Years. Yes, they may keep their ratio / percentage constant (although they can change it too) but KIBOR is purely based on the value set by Govt. So accordingly, banks have to adjust / manage accordingly, and are helpless in this regard.
I think, all such things are also mentioned in the terms and conditions, but we hardly bother to read them.
You may read terms and conditions, and then take action accordingly.