If your absence wasn’t connected to your disability then they don’t have to adjust for that and it will go on your absence record and can and will be used in dismissal processes.
I have a disability and have multiple adjustments as supported by OH and consultant. Still had to kick up a stink and get union in to get them in place.
however, I’ve also had a few absences not related to that disability (x2 covid a chest infection and a couple bouts of d&v - think patient facing healthcare and you get the gist)
they absolutely do go on my absence record as they should and I wouldn’t dream of asking my employers to ignore them because of my unrelated disability
(For fair comparison in my 36 mths I’ve had a total of 15 days off - I work p/t so the d&v 48hr rule usually knocks out a week, and is compulsory absence in NHS as was my first bout of Covid)
however…..
…. If… and I say if…. Your stress is proven to be linked to the hearing loss and tinnitus … then you may have an argument that by not allowing you to return and use the new headset may be a failure to make reasonable adjustments to see if your attendance /stress improved.
The onus is on the employer to proactively make adjustments as well - particularly when reasonably expected to know or assume the employee has a disability. The prolonged absence should have prompted them to consider if it was disability related and If they have not bothered to do that then there is also failure at that point.
finally if the OP has hearing loss then adjustments should also have been made to meetings she’s had to ensure all information given and received was fully and accurately communicated and understood by both parties as people with hearing loss can struggle to communicate effectively. and perhaps from the OPs post the person leading the meetings wasn’t really taking the OPs disability into consideration by ensuring effective communication
I think you absolutely right to have ACAS involvement but I would expect you to have a very clear account and timeline and well documented evidence of all the issues.
A union rep would be helpful if you have one.
in terms of tribunal - the judge may uphold some elements of a complaint for unfair dismissal and disability discrimination depending on facts but it’s not clear from your account - but probably not all so it may be at a deadlock.
Remember that if a tribunal finds a claim to be malicious or that your claim or conduct is unreasonable they May order you to pay costs so follow the ACAS advice carefully and be honest with them.
Finally, as a fellow hearing loss sufferer with hearing aids, I’m not sure I could cope with a phone job. I struggle enough in a semi patient facing environment and avoid phones, actively preferring teams to communicate. You may wish to consider if overall this was the best environment for you.