Possible malware on iPhone

Recently I was targeted and thieves managed to gain access to my bank by setting up a mobile app on their phone! I am not sure if they have access to my phone but I am not receiving all of my messages or notifications. My phone is often slow and overheats - I have been told all of this can be an indication that malware is on my phone. Can anyone give me a trusted and secure way to find out if this is the case? Thanks