I think the schedule below will work. All the matches should be different, teams play 4 times on each court (column), and teams play either 2 or 3 times in each of the three time slots (rows within each block of three).
(G F) (K L)
(A C) (B I)
(E H) (D J)
------------
(D A) (G E)
(J H) (L C)
(K I) (F B)
------------
(C H) (E J)
(G I) (K D)
(L F) (A B)
------------
(K E) (A F)
(L J) (I H)
(G B) (D C)
------------
(B H) (J I)
(D E) (K F)
(A L) (G C)
------------
(D B) (C I)
(L G) (A E)
(F J) (K H)
------------
(K C) (L B)
(F E) (A J)
(D I) (G H)
------------
(A I) (F H)
(B C) (D G)
(K J) (L E)
Alternatively, if you go for 9 rounds then you can have all teams exactly three times each at each time slot.
(K J) (L C)
(A D) (H E)
(F B) (G I)
------------
(H J) (A B)
(G C) (E I)
(F L) (K D)
------------
(H D) (F C)
(L B) (J I)
(G K) (E A)
------------
(K A) (F D)
(H C) (J B)
(E G) (L I)
------------
(E D) (G F)
(L A) (K B)
(H I) (J C)
------------
(I B) (E K)
(H F) (G A)
(L J) (C D)
------------
(E L) (G J)
(F K) (D I)
(C B) (H A)
------------
(C I) (H B)
(G D) (L K)
(E J) (F A)
------------
(A I) (G L)
(E C) (F J)
(D B) (H K)