Though i am not sure, but maybe their is an effect active that doesn't let you play a Spell Card.
Or have u read the requirements in the Fusion Monster card, as some cards like "Ryu Senshi" need the exact monsters (you can't use material substitute monsters for it).
To understand your problem properly, need to know what exactly you played and if possible what cards where there on the field.
Is there any "Poly" searcher in game yet?
I was already able to get 3 Poly's (1 from Joey's lvl up and the other 2 from Card Trader), but its been really hard to use them properly without a good searcher for 'material' or 'poly'.
There been many times when i get back-to-back 3 Poly's, but have no material monsters in hand, while other times i don't get the Poly itself, even if i have the mats.
Presently been trying to get Material Substitute cards to increase the chances of getting a Fusion out, but without a Poly its really hard.
Considering that we already have Arc-V Era cards like "Wonder Balloon" in the game, i would really like if they add Monsters with Poly effect in the game (if it isn't already there yet). Maybe something like either "Curse of Dragonfire" or "Fusion Parasite".
Is it possible at this point in the game to make a competitive fusion deck. like platinum quality. The way I see it is most fusion guys are level 6+ and if u manage to get 1 fusion guy out. U basically lose if he dies. Seems like ritual is way better because u can sacrifice anyone and some of them have actual effects.