An old boot is now uncomfortable - fallen arches?

[eeebby]

I am wondering if you are able to help me.

I am a long-standing customer of a respected shoe brand and have recently bought my second pair of their boots. They have a medium/small heel and I have always known the boots to be the most comfortable shoes I have ever worn. The sole fit the profile of my foot perfectly. Unfortunately, whilst I was waiting to purchase my new pair of boots, I was unable to wear the old pair as the sole had cracked (from excessive wear probably).

I am now finding that now I am wearing them again, my new pair of boots are causing pain to the arch of my foot, as the sole of the boot is pressing against my foot. I also put on my old boots and I have found that they also hurt, when they previously fit like a glove! It's almost as if my foot has become flatter and my feet no longer fit the curve of the boot, due to wearing flat shoes? I am absolutely devastated because these are my favorite ever boots that I could always rely on to be comfortable!

I was wondering if you had any advice of how I can wear my new boots as comfortably as my old ones? Is it dangerous to continue wearing these boots when they are causing me pain? Is it possible that the arch of my foot has fallen, and will I be able to correct it?