Change plan

Level 2
I have been with TPG from the start?
My current plan is 50gb peak + 50gb offpeak l have used all of my data and have tried on 30/3/20 31/3/20 talking to Chat? No results trying to change my Plan to unlimited with home phone. I go into my account ok!
Then into Change your Plan? Nothing happens from there. I can look at all of my account details but not Change your Plan.
My plan kicks back in 07/04/20 Eric