I have been working for a family run insurance office for the last few years. About a year ago I was involuntarily transfered to another office an hour away from my house. Because the awful manager had alienated 10 members of staff in 2 years (for context this is 100% turnover of their usual staffing level). To sweeten the deal because they were in a bind, and I was a hard to replace employee. They verbally agreed to pay my mileage (at a stupidly low rate, but because I was travelling 60 miles+ a day it added up). This was paid to me by transfer for months and it was no big deal. For a few months I forgot to claim, because of work pressures (they couldn't replace the employees who left) and when I submitted a request for 3 months at once they back paid with no issue.
So I submitted my request in April, and it was not paid, I challenged this and they assured me they would correct the error. They didn't, and due to cost of living pressures and generally unpleasant environment. Relations soured and I handed in my notice two weeks later, worked it and left. When I left I handed them an expense claim form for the missed payment in April plus three more months since to be back paid.
They are now refusing to pay the allowance advising it was a temporary adjustment payment. Without ever advising me of this and giving me no timescale or notice that payments were stopping. At this stage I am owed close to £800.
Before leaving I kept a photocopy of all my time sheets, expense claim forms and payslips, because they have a habit of creative accounting when it comes to wages. I also have my bank statements clearly detailing the payments for months (these were paid independently of my standard salary usually a week in advance)
Should I consider legal action, as there was never any agreement in writing? I live in NI (UK)