Issues with Iphone 4

I'm having a few issues with my Iphone 4 & hoping someone could help. It's running the latest IOS & is not jailbroken.

I'm unable to delete any text messages - when I try, all other text messages also disappear from my phone & it won't allow me to send a text (I can enter a contact & write the message but the 'send' button is greyed out). The only way I can send text messages again is to receive one from someone else - then all of the text messages come back, including the ones I just deleted.

Also, it keeps sending garbled text messages - ie when the receipient receives it, the message they get will be half of what I wrote & half of a text message I have sent them previously. This is extremely frustrating as I'm constantly having to re-send text messages.

Also, if I forget to lock my phone & don't touch it, it will often randomly call people in my contacts list.

Also quite often calls I receive will just go straight to voicemail, particularly if I'm using my phone at the time. I will be holding the phone so I know it doesn't ring at all - I'll just get a 'you have one new voice message' text.

I took it in to the Genius Bar & they said it was a software issue & restored it to factory settings but it is still doing it.

Is there any other way of fixing this? I need to have a reliable phone at this point.