Job Seekers still on my tax allowance

SO I claimed for job seekers back in Jan 23 and claimed for less than a month as I got a job in Feb. Now my issue is since cancelling my job seekers and receiving the p45 (which I passed to my new employer) I am being taxed on BR as HMRC still has my Job Seekers as my first employment. After contacting Job Seekers they advised it may not have been closed properly at their end and would make sure it was processed. This was 3 weeks ago and my code is still BR. I have tried calling HMRC numerous times but always get cut off while on hold. I'm losing nearly £300/month which I really need as a single parent, and I know it will come back to me eventually, but I need it now not later.

Hi,

I apologise if you are having issues getting this corrected. You will need to try and contact our helpline again.
We are less busy if you can call earlier in the day -
Income Tax: general enquiries

Thank you