Santander under funding fee

Was wondering if anyone else had this ?
I have an account with Santander - I’ve had it a while.... it’s an account I don’t use very much but anyway a few years back now I was constantly in its overdraft - I only paid about £150 a month into the account and it wasn’t enough to get me out of overdraft so for the full month every month I was in overdraft - so used to get charged £30 a month overdraft fees ... which is expected..... but I also used to get charged an underfunding fee on top which was around £25 (can’t remember fully) but as you can imagine i just got further and further into my overdraft every month.
Suddenly the underfunding fee stopped appearing on my statements —— so I’m wondeting if this was an unfair charge and they realised this and so stopped charging it and in which case can I claim this back from them?

Thanks in advance

Hope I posted this in the right area as it’s my first post on here x