Help problems with 3G network and internet connection

[chellz64]

Hello,

I have just changed my phone from an Optus Plan to Optus Prepaid today (using my old sim card which is a 3G post paid sim). I have a the Europa phone that I bought from UK (unlocked). I am unable to get any 3G signal or use the internet. This phone has been used in Malaysia last week and worked fine. No issues. Now I have been on the phone to Optus and Samsung both of whom cannot work out why there is no 3G signal and why I can't use the internet on my phone.

I can sms and make calls to other phones with no problem.

Am I correct to assume that if there is a 3G signal my phone should pick it up automatically?

Does anyone have any suggestions as I am getting tired to calling ppl who don't seem to know what is wrong.

Thanks in advance