wi-fi to 4g or 5g stuck

I have an iPhone 17 purchased on August 13th, and several times a day, after being connected to Wi‑Fi, when it’s supposed to switch to mobile data, it doesn’t connect and I lose mobile data completely. Sometimes after a phone call, it also loses data in the same way. The only way to fix it is by restarting the phone — I have to do this around 10 times a day.

I already spoke with my carrier (MEO in my case) and they say everything is fine. With Apple support, I’ve already done two support chats with multiple tests and nothing. They even scheduled an advanced support session, which also led nowhere, and after testing Apple says the problem is not with the phone.

I’m getting desperate and I urgently need a solution for my problem, but I’m lost.