Which high alcohol yeast did you use?
And did you add a couple of teaspoons of nutrient.
Tannin may also be another ingredient that would be useful.
The recipe you quote will have acid in it but not a great deal of nutrient so it would have benefited from some more. High alcohol yeast need extra.
Presently have a high alcolol mix going that is mead + raspberry, the SG was at 1.080 but additions of additional honey have made an equivalent SG of 1.140. Presently it is down to 1.008 and bubbling at a reasonable rate. It is checked and monitored almost daily.
Another problem is that if all the sugar goes in at the start then yeast tends to not reach it's full potential. Better to add in batches. You need a hydrometer to keep track of the gravity changes then.
2 kg is a lot of sugar so unless you had something capable of 21%, Gervin's GV4, and it was fed nutrient the mix you began with was almost destined for a sweetish wine.