Hello,
While I am no "legal eagle" I am not sure you will win this one, in the absence of documented evidence to support your claim on the arrangement with MBNA.
That said, I'd expect AdvantCard also have copy of this agreement - question is, can they find it or even more to the point, do they want to ?
If your' getting no where with AdvantCard - contact the Financial Services Ombudsman to make a complaint about their failure to communicate with you, they will give you some assistance with making contact (usually the Ombudsman's office begins their process by giving you the name and contact details of a nominated person in the bank, who you should write to regarding your complaint - if that party fails to resolve your problem, you go back to the Ombudsman and they make enquiries to subsequently make a ruling on the situation).
Sadly, there are a lot of us having problems with AdvantCard since they took over from MBNA - although it's more on the lack of customer service, than any similarity to your personal circumstances.
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In addition to making a complaint, I would also recommend you submit a Data Access Request, to AdvantCard seeking copy of all of your records at their offices - it will cost you €6.35 and you put the request in writting. They then have (I think it's) 40-days to provide you with copy of your file. This may help you evidence your claim
Regards
Mr. Earl