Mobile data no longer works, what should I do?

My mobile data on my (italian sim) doesn't work anymore i have a huawei with dualsim and the other one works great what can i do there?

Go to the settings for cellular network then check whether data roaming is still active.

How long have you been using the Sim outside of Italy?

Is active

one year approx.

Then it worked longer than the provider should allow, SIM cards from foreign providers only have to work for a certain period of time with free roaming, which is roughly the period in which you are on vacation abroad, if the SIM card is used longer the provider can use the free one End roaming in other EU countries, that's the fair use limit, and your provider has now apparently pulled the plug

https://www.teltarif.de/roaming/fair-use-policy.html