To be fair to HMRC...
"They are not going to give you money without you working for it, my friend. "
To be fair to HMRC, my experience over the last 10 years or so has always been positive if I've been due a refund. After the online SA calculation is produced, and if a refund is due I am asked to input my sort code and bank account number, and then the money has always been in my account within 7 days 'ish.
No real work or fighting has ever been needed.