Here is some practice online: https://www.gcflearnfree.org/edlmoney/pay-bills/1/
You can also find out how to pay bills online.
ATT has information here
You can google "How do I pay the _____ (name of company) bill online?" or "How do I pay the ____ by phone?"
Each company is only a little different.
Here is some help to understand: Using Google to Pay Bills Online
Here is some practice with writing large numbers in words. Write as many digits as you want. Try to write the words. The computer will show you if you are correct.