Got A LOT of spam calls

So I made an account in Oanda and to apply I am required to give my contact information which is normal. This also happens in a lot of brokerages. I was also required to give my phone number and again I think this is normal. I have applied in a lot of brokerages so it's fine, I know the drill. I give them my real phone number because I know that they will send me the OTP number. But, as soon as I applied I received a lot of phone calls from unknown numbers. I mean A LOT! I got spam calls from different countries. I don't know if they are selling your number to a third party or it was their marketing trying to sell you something. But it is annoying!