Change of Paid seat

Booked and paid for 2 seats with extra leg space on Dec 2018 and also received confirmation. When about to do check in today 9th March, notice that our seats had been changed to those that's without the extra leg space.
Called the customer service and they can't gave an explanation why our seat had been changed and furthermore received no notification.
After much persistence, the agent said she will changed back to the seat number we had paid\booked for and told us to wait for awhile but when we checked again, nothing had been done and we call back, the worst is that anyone that answer our call, they put us back immediately into holding mode....
You may check you call log system to verify base on the.

Question to Jetstar...
1 - How can this happen when we had booked and paid for the seat (Dec 2018) and even received a confirmation?
2 - Does the customer service has the right to pick and choose which call they want to answer?
3 - Is there an issue in the booking system?
4 - Is there no traceability on the booking system?