Unfair dismissal following allegation of inflated mileage claims

Is anyone able to offer me any advice. I have been dismissed from work following in excess of 30 years in the same company. Part of my duties were to visit customers in their own homes. I have to adhere to health and safety policies which mean that I have to locate the properties and park my vehicle legally in a position to exit the road etc. sometimes having to park away from the property due to parking restrictions etc. I have always planned the route using an A-Z and measured the mileage using my trip. The only detour would be on very rare occasions for petrol. I nor any of my colleagues have been advised that this method of arranging and recording mileage is not acceptable. Following an investigatory meeting with myself all staff in my particular team were advised that post codes of the properties visited needed to be entered in order that mileage could be checked, again no details provided as to how the mileage should be recorded except for the post code to be provided. I have been advised that the mileage that I recorded which is the actual mileage completed wholly in relation to my duties ( started and ended at work) was inflated against Google and it is classed as gross misconduct. The A-Z that I use was paid for by my employer.. I am in the process of taking the matter further. Any advice

Unfair dismissal following allegation of inflated mileage claims