Who have you been referred to in the NHS? You need someone who really understands this condition, many urologists (most, in fact) are woefully ill informed.
There are numerous ways to tackle this:
Long term antibiotics, low dose tends not to work, high dose is necessary for a good length of time. It’s very important to look after your gut health on this treatment, the best probiotics you can find, kimchi etc. Digestive issues caused by antibiotics can stop and thwart treatment. This happened to me.
Hiprex, often in combo with antibiotics, although it can work alone, but can take a long time to work. Not sure how long you took it?
Instillations of antibiotics done directly into the bladder, you can do these at home. Often resorted to by those whose digestive systems can no longer cope with high dose oral antibiotics. They can work, some people have great success, but they’re considered not as effective as oral antibiotics.
The uromone vaccine - this has a very variable success rate, some get no benefit, some are helped or get rid of symptoms altogether.
Some have success treating hypertonic pelvic floor which can mimic uti.
If you’re menopausal, using vaginal oestrogen is critical in case urogenital aspects of menopause play a role. For some people this is the root of their issues.
Treating thrush, common with antibiotic use, is critical, as thrush will exacerbate uti symptoms.
There are also a myriad of herbal remedies that have some evidence of efficacy.
From your post it looks like high dose oral antibiotics were working for you, you just need to be on them longer and you need a urologist who supports this. Some urologists in the embedded uti field don’t believe in testing as they think the actual bacteria causing the issue might be ‘hidden.’ In my experience, testing with one of the labs that does advanced testing has been helpful in guiding which antibiotic is likely to work, look at Focus labs or Regenerus. NHS tests are hopeless and often give false negative results.
There are some really helpful forums on Facebook, although some are very fixed on only one way of treating being the right way.
Feel free to DM me if you like.