Starhub Mobile

I used to have three mobile phone numbers in Starhub. One I used for business purpose, the other is the backup (due to the reason that sometimes my O2 phone is hanging it will forward important calls to the other one) and the last one is with my wife. When I decided to stop using O2 and used the old Nokia phone instead, my mobile phone cannot contacted at certain periods (maybe around 5 to 6pm) and the thing is I can call using my mobile phone but all callers will get a busy signal and will not even be diverted to the voicemail. I called customer service and I was just told that the starhub has no problem and it is my phone, he said maybe the SIM card is problematic. And the guy keep on insisting that it is not Starhub problem. What I understand is different, it is not me only having this problem, there are lots of my friends having this issue. Sad to say they have contract on their phones, mine doesn't so I transferred my business mobile to Singtel. And to make matters worse, when I decided to port my number (1 of my mobile is Powerconnect - monthly around 50sgd, the other is a new one - around 10sgd) they split first the Sharing plan and converted to two powerconnect (that is like 100sgd?!?). THe customer service officer mentioned that if I changed my remaining number (used to be 10sgd) to a lower plan, I need to pay another 10 dollars. Sad but it made my decision faster than ever, I transferred instead my two numbers. I now have 1 remaining starhub mobile being used by my wife.