Phone acting very very weird!

Hi all. Been having a problem with my phone for couple days, i will try to describe it best I can.

Phone is s6 edge on vodaphone.

I have had 200 dollars taken out my paypal account by "propellerads" company which i never heard of and had accessed my phone email. I thought its a virus so proceeded with a factory reset. After the factory reset, I had checked my messages to see that I have sent a message to a number I have never seen in my life "07480635445" containing 8 digits sent 4 times. I have called vodaphone and they have changed my phone number. After this,running various antivirus software no malware or viruses have been found. Today i woke up to be surprised to see that I have apparently sent to that number 4 times 8 digit message again. No malware or viruses are on the phone and messaging permissions has only the samsung messaging app. Any of you guys have any idea how or what could it be, as I am lost for ideas. Also quick note no apps or websites have been visited for me to get any viruses. Maybe sim card got hacked if that is possible? SS7? I am lost.