Plus not working

I got plus that expires next May I deleted and then re-download the app and I plus went away whenever I try to buy it back it says would you like to use your old subscription and I press yes and it says you’re all set and it brings him back to the screen where I can see all the plans so I do not have the plus and it’s not working. I would even re-buy it, but whenever I Cancel the subscription, it always comes back on the app, which makes no sense so please help