This is a dumb, and unecessarily hostile comment.
Dumb because: this isn't about accepting a certain payment method type. Revolut are a bank, a bank like any other. O2 not accepting Revolut would be like O2 not accepting payments from people with HSBC, or Santander, or any other major high-street bank.
Hostile because: really...? Telling OP they're risking debt collection and being unable to get credit elsewhere..? And frankly your cut and dry tone just makes you sound unpleasant, and unhelpful. You could ABSOLUTELY have expressed the same opinion in a constructive and helpful way, you could also have actually offered OP a solution to their issue, such as "it's not ideal, but you could always open up another bank account with a bank like Starling for the sake of paying your O2 bill, it only takes 5 minutes to open a Starling account. It's not a resolution to the Revolut problem, but at least you won't risk getting into trouble by delaying paying your bill."
It expresses the same (relevant...) key point in a constructive and polite way, and actually provides a solution.
OP is angry and frustrated, and rightfully so, but you seem to have taken that personally for some reason. OP was expressing public frustration towards O2, as people do, because it's mass expressions of opinions like this which often result in actual change- if enough people are frustrated and loud enough, it drastically increases the chances of their concerns being addressed. And it IS extremely frustrating that O2 completely arbitrarily do not accept payments from Revolut. The entire infrastructure of bank payments literally relies on businesses and vendors accepting payments from major banks (major = anything VISA, Mastercard- in the UK). Selectively refusing certain major banks completely destabilises the entire infrastructure, as soon as you need X card for A vendor and Y card for B business, the whole system goes to crap. It's completely counter-productive for their own business, as it runs the risk of losing custom from those who bank with, in this case, Revolut.
There's a reason that O2 are the exception, not the rule here. It's in every business' best interest to accept as many payment methods (or at least as many banks as possible). No matter how you spin it, it's exceedingly dumb for them NOT to accept payments from Revolut, and there is absolutely no good reason for them not to. Literally everyone is a loser. Of course Revolut are still relatively small compared to high-street banks, so there's no real urgency for them to sort it out, but it's almost like you're making out like they actually don't want to accept Revolut "entitled to choose which payment methods are acceptable to them", this sentence actively attributes intention... I absolutely promise you that not accepting Revolut is not a conscious choice made by O2 execs... It's more than likely just laziness, and being slow on the challenger bank uptake. They will eventually, beyond a shadow of a doubt, catch up and begin accepting Revolut, as I said, it would be extremely dumb for them to actively choose not to...
Remember the human... OP's tone is understandable, and it's not aimed at an individual. Your tone is unpleasant, and in direct response to OP. If you think their tone is not appropriate, find a constructive way of expressing that opinion, no need to get so defensive on a multi-billion pound corporation's behalf, trust me, O2 don't care about someone moaning about their service, they undoubtedly endure far worse on a daily basis lmao
Edit: SHEESH I really wrote that much huh... For the record, it's not that I care THAT MUCH, I just really can't be concise in writing, and I do kinda just enjoy writing, regardless of what it's about. I get waaaaaay too carried away...
