Billing problem and apple id not valid

Every time I try to install an app or update, It says theres a billing problem. I've cancelled all subscriptions and even bought a gift card. And every time I try to see the billing problem by putting in my apple ID, it always say invalid id. I know its the correct id because Ive changed it. Ive already resetted my device and everything. This is really starting to get on my nerves atp. Please fix this problem apple.