What's more important is whether they have professional indemnity insurance. Regulated "chartered" accountants must have it but unqualified/unchartereds don't have to and many choose not to bother, leaving their clients exposed if the accountant fouls up costing you money.
Also, if you ever want a mortgage or loan or want to rent a house or business premises, etc., many lenders/landlords want a reference from a qualified accountant, so if yours isn't, then it may jeopardise your chances of borrowing money or renting property.
But, back to basics, what made you think they were "chartered" and why do you now think they aren't? If they're openly advertising themselves as chartered on their website, adverts, etc., then not only can you complain to the chartered bodies, but you can also complain to your local Trading Standards about misrepresentation.
At the end of the day, there's an easier and stress free way for you - that's to change accountant to someone who is "chartered" - all the changeover is handled by the new accountant so hassle free for you.