Well, if you really want a solution, PayPal have registered offices inside the EU to which you can write an old fashioned letter. Simply state they hold incorrect information (old phone number) & demand they correct it under the provisions of the GDPR. I suggest registered post, so someone has to sign, if that fails, repeat the letter, second time from your solicitor & threatening legal action. This was going to be my ultimate strategy, except that I've managed for now to solve the issue using one of the methods listed in the first reply.
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