My account doesnt let me buy champs even though i have enough ip

I was planning to but darius and he is 4800 ip right so i gather up and i have about 7000 ip and when i click unlock it doesnt let me it says not yet implemented i had this for the whole season 7 and whenever i want to buy champs i have to go to my friends house because theres work.riot and ever since i upgrade to season 7 it didnt work at all i even submit a request in support riotgames but they didnt anwser.