Offshore overdraft, pay Thai stamp duty?

I've been trying to arrange a Sterling overdraft facility with my bank (Barclays) in Jersey. Initially they were falling over themselves to do it, but now they suddenly seem to be back-pedalling, and I've no idea why. Their latest excuse not to do it is that as I live in Thailand I will have to pay 0.05% stamp duty on the overdraft total. I told them that I don't mind paying the stamp duty as long as they could provide me with a tax certificate from the Thai authorities saying that it had been paid. They haven't responded to that request. they just replied saying how complicated it all is. This sounds like nonsense to me, but I'd like to check if it's true before I get back to the bank. Does anybody know if this tale about having to pay Thai stamp duty on overseas loans which are completely unrelated to Thailand is correct or not?

Some background: I stay in Thailand on retirement extensions, and I don't work or pay tax here, other than the 15% withholding tax on bank interest which I reclaim every year. The overdraft in Jersey is effectively a bridging loan for two months to allow me to make an offshore Sterling investment which has nothing to do with Thailand.

Thanks for any help.