Unable to receive emails - relaying disallowed

HI there,

I've changed hosting provider yesterday and since then I haven't been able to receive emails.

At first I was getting this message:

Each of the following recipients was rejected by a remote mail server. The reasons given by the server are included to help you determine why each recipient was rejected.

Recipient: <natasa@milevvamarketing.com>
Reason: 5.1.1 <natasa@milevvamarketing.com>: Recipient address rejected: User unknown in virtual alias table

Reporting-MTA: dns; sa-prd-fep-041.btmx-prd.synchronoss.net
Arrival-Date: Mon, 25 May 2020 11:02:17 +0100
Received-From-MTA: dns; sa-prd-rgout-002.btmx-prd.synchronoss.net (10.2.38.5)

Final-Recipient: RFC822; <natasa@milevvamarketing.com>
Action: failed
Status: 5.1.1
Remote-MTA: dns; mail.milevvamarketing.com (185.5.172.158)
Diagnostic-Code: smtp; 550 5.1.1 <natasa@milevvamarketing.com>: Recipient address rejected: User unknown in virtual alias table

I then contacted the new host, who changed their records... But today I'm receiving this failed message:

Each of the following recipients was rejected by a remote mail server. The reasons given by the server are included to help you determine why each recipient was rejected.

Recipient: <natasa@milevvamarketing.com>
Reason: Relaying disallowed

Reporting-MTA: dns; sa-prd-fep-043.btmx-prd.synchronoss.net
Arrival-Date: Tue, 26 May 2020 10:02:56 +0100
Received-From-MTA: dns; sa-prd-rgout-003.btmx-prd.synchronoss.net (10.2.38.6)

Final-Recipient: RFC822; <natasa@milevvamarketing.com>
Action: failed
Status: 5.1.3
Remote-MTA: dns; mx.zoho.com (136.143.190.121)
Diagnostic-Code: smtp; 553 Relaying disallowed

I contacted the host again just now but they are now saying they've done everything they should, that their records are now correct and that I should contact you instead... Please help!