You’re right 
Tom said at a recent talk that Monzo is planning to double their number of staff next year & they will be moving into a new office too 
If you want to join the team, check out the careers page -
Also, one of the things Tom said he was most proud of, was the quick average response time of the support team, through the in-app chat. In order to ensure that they don’t get swamped by the surge in the number of users that will (hopefully) result from the current account launch, Monzo will ‘overstaff’ their support team initially. So they will definitely be recruiting more people for that team 
Interestingly, Leah mentioned in a recent podcast that they take a very different approach to building a support team than most companies.
Rather than hiring as cheaply as possible, Monzo want to hire people who can actually fix any recurring problems that’re caused by issues with their systems & processes, rather than simply explaining the problem, providing a workaround and apologising 