RHA T20 Headphones Snapped Wire

Your expectation of warranty entitlement indicates you believe the cause to be a robustness issue rather than owner clumsiness, and certainly the product is not cheap tat with low robustness expectation when the manufacturer uses descriptive quality/robustness/durability/longevity phrases including

better materials
outstanding durability
every component is engineered by our team to achieve the highest quality performance
premium materials
lasting quality
long-wearing durability

In which case why bother with warranty?
Just present your Consumer Rights Act claim to the shysters that sold you the quality and durability-lacking prematurely-failed rubbish.
You have six years to present your lack-of-durability claim to the merchant (and/or possibly credit provider), unless you live in a country that shafts its citizens by insisting on a lesser period to claim, such as Scotland.
Example standard claim template via respected consumer mag "Which" at:
which.co.uk/con…lgZ

It looks like that break is at a very awkward place (at the moulded Y piece) and so would be very hard to repair. I am not surprised RHA are reluctant. The easiest solution (in my opinon) would be to replace the complete cable. As the T20 ear pieces do not have removable cables - this would mean cutting the cable on each side, some way below the ear pieces and soldering in a new cable, protected by heat shrink tubing at the joint to add durability. The cable could come from any old IEM and a phone shop technician would probably be happy to do this for you if you cannot solder.

Depending on the extent of damage on both sides, you might be able to take them to a repair kiosk/shop that do phone repairs, etc.

What they'll do is strip the cable and resolder them onto where they separate (or on the other side of the cable).

However, I've only done home-based tinkering myself and I am not an technician (of this sort), however they will have a phone number for their business and it can't hurt to enquire about it. (edited)