This is sad and scary, and unfortunately very common. Be careful when you go to these big chain referral centres and when a vet asks you how high your insurance cover is
I met another Brit travelling in Thailand who went to hospital with a stomach problem. They didn't want to treat him until they got a confirmation email from his travel insurance. After they got the email they gave him a massive room to himself, lavished loads of food and drink on him and wouldn't let him leave after he got better.
We also maxed out the limit twice. 10k for us. Went 2k over the first time. Second time is this year so hoping he doesn't need anything expensive before June. He's has 2 total hip replacements at £8500 each.
Ours is an independent clinic, they're staffed 24/7 and have always been lovely. Never ask us to come in if they don't think it's necessary, ask us to send pics before we come in out of hours so we can potentially avoid the extra fees etc. They're quite a while away from where we live but we're happy to travel a bit