Hi i am wondering if i can have some advice, i think this may be a phone problem rather than a network problem, but people abroad do not receive messages from me when i send them (all the time) and I receive messages multiple times sometimes, which indicates that my phone is not signalling to other networks that it’s received messages.
Then I would try a new SIM card. SIM card get defunct pretty fast, unfortunately… But contacting your network operator also might be a good idea. I feel that the community can’t help you with this here on the forum…
Just to be sure: you are talking about standard text messages (SMS), using the standard “Messages” app?
Considering messages not arriving at your contact’s side: you’ve got the right country code, there’s no additional prefix you need to drop or add, (in Germany, that would mean dropping a 0 in front of the city code, but I experienced that this differs in other countries even based on the operator, e.g. a 1 after the country code would indicate a specific network and would curiously have to be dropped in some cases AFAIR), and they used to receive the messages when you were using the Fairphone already?