Noticed theres a bit of dangly wire on the
left side, and the wire on the right is taught and now theres none on
the "rolly bit" at the top.

Cable broken. New cone/cable sets around 20-30 per pair. Replace both.

You could DIY, but your local specialist will probably supply and fit both
for around twice that. Worth it just to avoid big springy things! Don't
contact the big companies, they'll just try and sell you a new door for 500
quid.

Al.