You can try calling 211 or 7301300 and have your plan recontracted. it’s swift and hassle free. Just make sure ask a whole lot of questions to avoid miscommunication.
I was able to recontract last Feb 2017 with CTB (charge to bill) iPhone 7 with 1 yr and 2 months tenure and that’s also through 7301300. Let me know if this helps.
PS. When I recontracted for iPhone XS, they automatically processed the increase of my credit limit even tho my salary isnt 50k and it’s approved right away. I think one thing they consider aside from the salary is your credibility in paying your bill (if you settle your payment on or before due date).