I've asked numerous times for advisory work but I've been given nothing. As for a development plan there is nothing in place, been told I need to qualify to get some advisory work but when I look at the tax seniors in my firm they're also not doing advisory.
Gosh, that very much sounds like your employer is the issue not tax. I think you've been let down.
After 3 years I'd expect you to have been supported and encouraged to qualify, maybe even be on the cusp of being dual qualified.
I'd expect you to be invited to client meetings even if just as a note taker initially, to be involved in ad hoc advisory as opportunities arise, and to have a clear path beyond doing data entry.
This has led to me stop studying for my exams as I see no incentive to finish them.
The incentive is that it would make it easier for you to jump ship and work for a better firm doing more interesting work! You have to take some responsibility for making yourself valuable and marketable if you want to progress to more interesting work.
What does your employer say about you stopping? Surely that prompted a discussion? If any of our trainees just stopped studying for their exams it would trigger discussion and action. What happened when you stopped?
I can only assume you're working in a regional office for a top 20 rather than a flagship location? Even for the big names, unfortunately it can be very office specific whether a regional office is a good place to build a career - or just where the London office sends their drudge work. (Some of them openly use that as a selling point in their job adverts when recruiting for London roles.)
You might actually have had a better experience at a top 30/40/50 firm than at a small regional compliance factory for a big firm.
I think it would be worth speaking to a reputable tax recruiter in your area who knows the local offices / firms well and can advise whether there's a better match near you. If nothing else it would confirm for you whether leaving tax entirely is the right answer for you or just leaving your current employer.