how to report coverage issue? my place having this issue since a month ago, incoming call hard to go through, slow internet

i am umobile prepaid user now
1) how i can switch to umobile postpaid easily?
2) after switch, is there any contract that stop me from terminating my postpaid subscription?
3) what happen to my existing prepaid credit after i switch to postpaid?
4) let say i have excess payment for my postpaid bill, what happen to my excess payment if i terminate my postpaid service?