hi guys, i've been over paying tax for the last few years, i want to claim it back and wondered if anyone on here has been in a similar situation and claimed it back successfully?

the website wants me to write to them explaining how i think i've over paid and including relevant documents but i'm sure i'd heard of people just calling up and it being worked out over the phone. i tried calling them this afternoon but i'm on pay as you go and after 5 minutes of listening to a machine i gave up but writing in seems like so much more hassle (especially as i am bad at maths and have no idea how much i've overpaid, i just KNOW i have). is there a better number to ring? should i have stayed on the line for 2 minutes more? relate your own experience/advise me please!