Samsung A42 5G displays "number not valid" when I am trying to call one specific number

[magz123]

I am having an unusual problem, I have tried everything to fix it and nothing has worked. When I try and call this one specific phone number my phone will display "number not valid". I have tried the sim in a different phone and it works, so it's not the sim card. I have tried a new sim in the phone itself and it still doesn't work. I can call other numbers from the Samsung and they work fine. I have tried altering the network settings specific for my network and that doesn't work either. I have tried calling from a different phone and it works. It is simply an issue that occurs when I try and call this specific number from my Samsung A42 5G, so I believe there is an issue with the device, I am very puzzled. I haven't blocked the number either and I don't have any other number blockers installed on the phone. Any suggestions? 

[Flintstone]

if it is a number in the country you are remove the country code and add a zero , sometimes that helps. (first just try it out with calling via the number key pad)
is it a service number of your simcard provider try the same

also remove dots spaces and dashes from the phone number. other option try phoning it with 4g and 5g disabled, another reason is maybe it is some other kind of special or redirected number. hope it helps

[magz123]

Thank you for the response. I have tried everything I can think of including changing the format of the number and that hasn't helped either. I have factory reset the phone and the problem is fixed for a time but then occurs again. The same happens when I restart the phone, the issue is fixed then returns when the phone has been on for a time. It's very puzzling. I have contacted my network to see if it is something on their end but at this point it may be a case of just switching networks to avoid this issue, there simply doesn't seem to be a fix. 

[Flintstone]

not sure what it is happening. there must be something special about the number, could be a redirect number, a number from a separate phone provider (some companies use them) a Skype or something like that number,

maybe try to phone the number plus or minus 1 or 2 (apologises if somebody answers the phone) check the number online maybe that gives a clue , I am a bit stunned

[magz123 · Accepted solution]

Nothing worked, so I had to change to a new sim card. Very strange error. Thank you for your help anyway.