Could be that the stamp is out of date for the valve type, afaik there is no twin "surface valve" set up.
Some places used to give 5 years on shooters cylinders even though the they actually had underwater valves, done "as a favour to the shooter" kind of thing as they knew the cyl was only used on the surface,
but a different shop can say that was not correct as the underwater valve must be tested at 30months, which is quite correct.
If it's not that then you need to clearly get the reason they refused, ask them to write it down quoting whatever rule.