Firstly I think the money has to be in the account for 3 months (I think). You might want to check that. Also bank letter has to be issued within 72 hours of you visiting immigration. You may need to do a new one.
Visa Exemption is different to 45 day visa ‘on arrival’.  If you do visa on arrival you will get 45 days and can extend for another 30 days and you could get another visa on arrival when u come back however you may get questioned by immigration
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