Mend a hole in an expansion vessel?

I have solar panels attached to the roof of my home in Spain. At the moment I should be enjoying the benefit of the free hot water that it generates.

Several weeks ago the vessel sprung a leak that I managed to plug. Unfortunately, it didn't hold out for long and the hole is a lot bigger. One this occasion the hole is too big to plug and I've had to turn off my water supply.

When I first discovered the hole I contacted the company who installed the system, but they didn't respond.

I am looking for an 18 SMF P.MAX:10BAR 18LTR WATER/AIR P.TEST:15BAR -10+130C P.PRE:2,5 bar
USE: SOLAR EXPANSION.

I would like to know if someone could tell me if it's possible to replace the vessel I have with a 3 or 3,5 bar vessel, as they seems to be the only vessels I can find on the internet.

Kind regards,