Wtf is going on with my taxes? Am i being overtaxed at my employer?

Okay so basically i was with my employer from May of this year (although i left this week and now moving onto another position). I am not too sure of what my tax code is as it’s just an a nightmare getting through to hmrc and i kept getting cut off and left on hold for an hour.
My taxes with my new employer seem unusually high, i’ve had many jobs in the past but it just seems extortionately high. The salary was meant to be £25,500 pa paid on the 31st then with the commission paid on the 15th of the month. The commission is also taxed and is around £250-£500 every month. Last time I checked online the take how pay for this salary should usually be around £1750 for the basic but mine is significantly lower which i find strange. Is this normal? I also haven’t been a uni student since 2015 and had a regular student loan so i’m not too sure why the student loan tax is always so high either. It’s not letting me post a photo but basically my last payslip for example said my base pay was £2125 that month, then there’s £311 PAYE tax, £177 national insurance, £88 ee pension, and £96 going towards student loan so i ended up only getting £1455.28 which is the same amount as the month before - which is imo a very large amount of tax. I was a full time employee if that made any difference, with a European passport but have lived in the Uk since age 4 and have settled status. On my payslip it says that my tax code is 1257l but i’m not sure this is right